CC2420 2.4 GHz IEEE 802.15.4 / ZigBee-ready RF Transceiver Applications 2.4 GHz IEEE 802.15.4 systems ZigBee systems Home/building automation Industrial Control Wireless sensor networks PC peripherals Consumer Electronics Product Description The CC2420 is a true single-chip 2.4 GHz IEEE 802.15.4 compliant RF transceiver designed for low power and low voltage wireless applications. CC2420 includes a digital direct sequence spread spectrum baseband modem providing a spreading gain of 9 dB and an effective data rate of 250 kbps. The CC2420 is a low-cost, highly integrated solution for robust wireless communication in the 2.4 GHz unlicensed ISM band. It complies with worldwide regulations covered by ETSI EN 300 328 and EN 300 440 class 2 (Europe), FCC CFR47 Part 15 (US) and ARIB STD-T66 (Japan). features reduce the load on the host controller and allow CC2420 to interface low-cost microcontrollers. The configuration interface and transmit / receive FIFOs of CC2420 are accessed via an SPI interface. In a typical application CC2420 will be used together with a microcontroller and a few external passive components. CC2420 is based on Chipcon’s SmartRF03 technology in 0.18 m CMOS. The CC2420 provides extensive hardware support for packet handling, data buffering, burst transmissions, data encryption, data authentication, clear channel assessment, link quality indication and packet timing information. These Key Features True single-chip 2.4 GHz IEEE 802.15.4 compliant RF transceiver with baseband modem and MAC support DSSS baseband modem with 2 MChips/s and 250 kbps effective data rate. Suitable for both RFD and FFD operation Low current consumption (RX: 18.8 mA, TX: 17.4 mA) Low supply voltage (2.1 – 3.6 V) with integrated voltage regulator Low supply voltage (1.6 – 2.0 V) with external voltage regulator SWRS041c Programmable output power No external RF switch / filter needed I/Q low-IF receiver I/Q direct upconversion transmitter Very few external components 128(RX) + 128(TX) byte data buffering Digital RSSI / LQI support Hardware MAC encryption (AES-128) Battery monitor QLP-48 package, 7x7 mm Complies with ETSI EN 300 328, EN 300 440 class 2, FCC CFR-47 part 15 and ARIB STD-T66 Powerful and flexible development tools available Page 1 of 85 CC2420 Table of contents 1 Abbreviations _________________________________________________________________ 5 2 References ___________________________________________________________________ 6 3 Features _____________________________________________________________________ 7 4 Absolute Maximum Ratings _____________________________________________________ 8 5 Operating Conditions __________________________________________________________ 8 6 Electrical Specifications ________________________________________________________ 9 6.1 Overall ___________________________________________________________________ 9 6.2 Transmit Section ___________________________________________________________ 9 6.3 Receive Section ___________________________________________________________ 10 6.4 RSSI / Carrier Sense _______________________________________________________ 11 6.5 IF Section ________________________________________________________________ 11 6.6 Frequency Synthesizer Section _______________________________________________ 11 6.7 Digital Inputs/Outputs ______________________________________________________ 12 6.8 Voltage Regulator _________________________________________________________ 13 6.9 Battery Monitor ___________________________________________________________ 13 6.10 Power Supply _____________________________________________________________ 13 7 Pin Assignment ______________________________________________________________ 15 8 Circuit Description ___________________________________________________________ 17 9 Application Circuit ___________________________________________________________ 19 9.1 Input / output matching _____________________________________________________ 19 9.2 Bias resistor ______________________________________________________________ 19 9.3 Crystal __________________________________________________________________ 19 9.4 Voltage regulator __________________________________________________________ 19 9.5 Power supply decoupling and filtering _________________________________________ 19 10 IEEE 802.15.4 Modulation Format ____________________________________________ 24 11 Configuration Overview _____________________________________________________ 25 12 Evaluation Software ________________________________________________________ 26 13 4-wire Serial Configuration and Data Interface __________________________________ 27 13.1 Pin configuration __________________________________________________________ 27 13.2 Register access ____________________________________________________________ 27 13.3 Status byte _______________________________________________________________ 28 13.4 Command strobes _________________________________________________________ 29 13.5 RAM access ______________________________________________________________ 29 13.6 FIFO access ______________________________________________________________ 31 13.7 Multiple SPI access ________________________________________________________ 31 14 Microcontroller Interface and Pin Description ___________________________________ 32 14.1 Configuration interface _____________________________________________________ 32 14.2 Receive mode_____________________________________________________________ 33 14.3 RXFIFO overflow _________________________________________________________ 33 14.4 Transmit mode ____________________________________________________________ 34 14.5 General control and status pins _______________________________________________ 35 15 Demodulator, Symbol Synchroniser and Data Decision ___________________________ 35 16 Frame Format _____________________________________________________________ 36 16.1 Synchronisation header _____________________________________________________ 36 16.2 Length field ______________________________________________________________ 37 16.3 MAC protocol data unit _____________________________________________________ 37 16.4 Frame check sequence ______________________________________________________ 38 SWRS041c Page 2 of 85 CC2420 17 RF Data Buffering __________________________________________________________ 39 17.1 Buffered transmit mode _____________________________________________________ 39 17.2 Buffered receive mode ______________________________________________________ 39 17.3 Unbuffered, serial mode ____________________________________________________ 40 18 Address Recognition ________________________________________________________ 41 19 Acknowledge Frames _______________________________________________________ 41 20 Radio control state machine __________________________________________________ 43 21 MAC Security Operations (Encryption and Authentication) _______________________ 45 21.1 Keys ____________________________________________________________________ 45 21.2 Nonce / counter ___________________________________________________________ 45 21.3 Stand-alone encryption _____________________________________________________ 46 21.4 In-line security operations ___________________________________________________ 46 21.5 CTR mode encryption / decryption ____________________________________________ 47 21.6 CBC-MAC_______________________________________________________________ 47 21.7 CCM ___________________________________________________________________ 47 21.8 Timing __________________________________________________________________ 48 22 Linear IF and AGC Settings __________________________________________________ 48 23 RSSI / Energy Detection _____________________________________________________ 48 24 Link Quality Indication______________________________________________________ 49 25 Clear Channel Assessment ___________________________________________________ 50 26 Frequency and Channel Programming _________________________________________ 50 27 VCO and PLL Self-Calibration _______________________________________________ 51 27.1 VCO____________________________________________________________________ 51 27.2 PLL self-calibration ________________________________________________________ 51 28 Output Power Programming _________________________________________________ 51 29 Voltage Regulator __________________________________________________________ 51 30 Battery Monitor ____________________________________________________________ 52 31 Crystal Oscillator___________________________________________________________ 53 32 Input / Output Matching _____________________________________________________ 54 33 Transmitter Test Modes _____________________________________________________ 55 33.1 Unmodulated carrier _______________________________________________________ 55 33.2 Modulated spectrum _______________________________________________________ 56 34 System Considerations and Guidelines _________________________________________ 57 34.1 Frequency hopping and multi-channel systems ___________________________________ 57 34.2 Data burst transmissions ____________________________________________________ 57 34.3 Crystal accuracy and drift ___________________________________________________ 57 34.4 Communication robustness __________________________________________________ 57 34.5 Communication security ____________________________________________________ 57 34.6 Low-cost systems __________________________________________________________ 58 34.7 Battery operated systems ____________________________________________________ 58 34.8 BER / PER measurements ___________________________________________________ 58 35 PCB Layout Recommendations _______________________________________________ 59 36 Antenna Considerations _____________________________________________________ 59 37 Configuration Registers _____________________________________________________ 61 38 Test Output Signals _________________________________________________________ 81 39 Package Description (QLP 48) __________________________ Error! Bookmark not defined. 40 Recommended layout for package (QLP 48) ______________ Error! Bookmark not defined. SWRS041c Page 3 of 85 CC2420 40.1 40.2 40.3 40.4 41 Package thermal properties __________________________ Error! Bookmark not defined. Soldering information ______________________________________________________ 83 Plastic tube specification ____________________________ Error! Bookmark not defined. Carrier tape and reel specification _____________________ Error! Bookmark not defined. Ordering Information _________________________________ Error! Bookmark not defined. 42 General Information ________________________________________________________ 84 42.1 Document History _________________________________________________________ 84 42.2 Product Status Definitions ___________________________ Error! Bookmark not defined. 43 Address Information __________________________________ Error! Bookmark not defined. 44 TI Worldwide Technical Support _______________________ Error! Bookmark not defined. Important Notice ___________________________________________ Error! Bookmark not defined. SWRS041c Page 4 of 85 CC2420 1 Abbreviations ADC AES AGC ARIB BER CBC-MAC CCA CCM CFR CSMA-CA CTR CW DAC DSSS ESD ESR EVM FCC FCF FIFO FFCTRL HSSD IEEE IF ISM ITU-T - I/O I/Q kbps LNA LO LQI LSB MAC MFR MHR MIC MPDU MSDU NA NC O-QPSK PA PCB PER PHY PHR PLL PSDU QLP RAM RBW RF RSSI - Analog to Digital Converter Advanced Encryption Standard Automatic Gain Control Association of Radio Industries and Businesses Bit Error Rate Cipher Block Chaining Message Authentication Code Clear Channel Assessment Counter mode + CBC-MAC Code of Federal Regulations Carrier Sense Multiple Access with Collision Avoidance Counter mode (encryption) Continuous Wave Digital to Analog Converter Direct Sequence Spread Spectrum Electro Static Discharge Equivalent Series Resistance Error Vector Magnitude Federal Communications Commission Frame Control Field First In First Out FIFO and Frame Control High Speed Serial Debug Institute of Electrical and Electronics Engineers Intermediate Frequency Industrial, Scientific and Medical International Telecommunication Union – Telecommunication Standardization Sector Input / Output In-phase / Quadrature-phase kilo bits per second Low-Noise Amplifier Local Oscillator Link Quality Indication Least Significant Bit / Byte Medium Access Control MAC Footer MAC Header Message Integrity Code MAC Protocol Data Unit MAC Service Data Unit Not Available Not Connected Offset - Quadrature Phase Shift Keying Power Amplifier Printed Circuit Board Packet Error Rate Physical Layer PHY Header Phase Locked Loop PHY Service Data Unit Quad Leadless Package Random Access Memory Resolution BandWidth Radio Frequency Receive Signal Strength Indicator SWRS041c Page 5 of 85 CC2420 RX SHR SPI TBD T/R TX VCO VGA 2 [1] - Receive Synchronisation Header Serial Peripheral Interface To Be Decided / To Be Defined Transmit / Receive Transmit Voltage Controlled Oscillator Variable Gain Amplifier References IEEE std. 802.15.4 - 2003: Wireless Medium Access Control (MAC) and Physical Layer (PHY) specifications for Low Rate Wireless Personal Area Networks (LR-WPANs) http://standards.ieee.org/getieee802/download/802.15.4-2003.pdf [2] NIST FIPS Pub 197: Advanced Encryption Standard (AES), Federal Information Processing Standards Publication 197, US Department of Commerce/N.I.S.T., November 26, 2001. Available from the NIST website. http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf [3] R. Housley, D. Whiting, N. Ferguson, Counter with CBC-MAC (CCM), submitted to NIST, June 3, 2002. Available from the NIST website. http://csrc.nist.gov/CryptoToolkit/modes/proposedmodes/ProposedModesPag e.html SWRS041c Page 6 of 85 CC2420 3 Features 2400 – 2483.5 MHz RF Transceiver Direct Sequence Spread Spectrum (DSSS) transceiver 250 kbps data rate, 2 MChip/s chip rate O-QPSK with half sine pulse shaping modulation Very low current consumption (RX: 18.8 mA, TX: 17.4 mA) High sensitivity (-95 dBm) High adjacent channel rejection (30/45 dB) High alternate channel rejection (53/54 dB) On-chip VCO, LNA and PA Low supply voltage (2.1 – 3.6 V) with on-chip voltage regulator Programmable output power I/Q low-IF soft decision receiver I/Q direct up-conversion transmitter Separate transmit and receive FIFOs 128 byte transmit data FIFO 128 byte receive data FIFO Very few external components Only reference crystal and a minimised number of passives No external filters needed Easy configuration interface 4-wire SPI interface Serial clock up to 10 MHz 802.15.4 MAC hardware support: Automatic preamble generator Synchronisation word insertion/detection CRC-16 computation and checking over the MAC payload Clear Channel Assessment Energy detection / digital RSSI Link Quality Indication Full automatic MAC security (CTR, CBC-MAC, CCM) 802.15.4 MAC hardware security: Automated security operations within the receive and transmit FIFOs. CTR mode encryption / decryption CBC-MAC authentication CCM encryption / decryption and authentication Stand-alone AES encryption Development tools available Fully equipped development kit Demonstration board reference design with microcontroller code Easy-to-use software for generating the CC2420 configuration data Small size QLP-48 package, 7 x 7 mm Complies with EN 300 328, EN 300 440 class 2, FCC CFR47 part 15 and ARIB STD-T66 SWRS041c Page 7 of 85 CC2420 4 Absolute Maximum Ratings Parameter Min. Max. Units Supply voltage for on-chip voltage regulator, VREG_IN pin 43. -0.3 3.6 V Supply voltage (VDDIO) for digital I/Os, DVDD3.3, pin 25. -0.3 3.6 V Supply voltage (VDD) on AVDD_VCO, DVDD1.8, etc (pin no 1, 2, 3, 4, 10, 14, 15, 17, 18, 20, 26, 35, 37, 44 and 48) −0.3 2.0 V Voltage on any digital I/O pin, (pin no. 21, 27-34 and 41) -0.3 VDDIO+0.3, max 3.6 V Voltage on any other pin, (pin no. 6, 7, 8, 11, 12, 13, 16, 36, 38, 39, 40, 45, 46 and 47) -0.3 VDD+0.3, max 2.0 V 10 dBm 150 C 260 C Input RF level Storage temperature range −50 Reflow solder temperature The absolute maximum ratings given above should under no circumstances be violated. Stress exceeding one or more of Condition T = 10 s the limiting values may cause permanent damage to the device. Caution! ESD sensitive device. Precaution should be used when handling the device in order to prevent permanent damage. 5 Operating Conditions Parameter Min. Supply voltage for on-chip voltage regulator, VREG_IN pin 43. Typ. Max. Units 2.1 3.6 V Supply voltage (VDDIO) for digital I/Os, DVDD3.3, pin 25 . 1.6 3.6 V The digital I/O voltage (DVDD3.3 pin) must match the external interfacing circuit (e.g. microcontroller). Supply voltage (VDD) on AVDD_VCO, DVDD1.8, etc (pin no 1, 2, 3, 4, 10, 14, 15, 17, 18, 20, 26, 35, 37, 44 and 48) 1.6 2.0 V The typical application uses regulated 1.8 V supply generated by the on-chip voltage regulator. Operating ambient temperature range, T A −40 85 C 1.8 SWRS041c Condition Page 8 of 85 CC2420 6 Electrical Specifications Measured on CC2420 EM with transmission line balun, T A = 25 C, voltage regulator used if nothing else stated. 6.1 Overall Parameter Min. RF Frequency Range 2400 6.2 DVDD3.3 and VREG_IN = 3.3 V, internal Typ. Max. Unit Condition / Note 2483.5 MHz Programmable in 1 MHz steps, 5 MHz steps for compliance with [1] Max. Unit Condition / Note Transmit Section Parameter Min. Typ. Transmit bit rate 250 250 kbps As defined by [1] Transmit chip rate 2000 2000 kChips/s As defined by [1] Nominal output power -3 dBm Delivered to a single ended 50 load through a balun. 0 [1] requires minimum –3 dBm Programmable output power range 24 dB The output power is programmable in 8 steps from approximately –24 to 0 dBm. -44 dBm -64 dBm Measured conducted with 1 MHz resolution bandwidth on spectrum analyser. At max output power delivered to a single ended 50 load through a balun. See page 54. 30 - 1000 MHz 1– 12.75 GHz 1.8 – 1.9 GHz 5.15 – 5.3 GHz -56 -44 -56 -51 dBm dBm dBm dBm Complies with EN 300 328, EN 300 440, FCC CFR47 Part 15 and ARIB STD-T-66 Error Vector Magnitude (EVM) 11 % Measured as defined by [1] Harmonics 2nd harmonic rd 3 harmonic Spurious emission Maximum output power. [1] requires max. 35 % Optimum load impedance 95 + j187 SWRS041c Differential impedance as seen from the RF-port (RF_P and RF_N) towards the antenna. For matching details see the Input / Output Matching section on page 54. Page 9 of 85 CC2420 6.3 Receive Section Parameter Min. Typ. -90 -95 Max. Unit Condition / Note dBm PER = 1%, as specified by [1] Receiver Sensitivity Measured in a 50 single-ended load through a balun. [1] requires –85 dBm Saturation (maximum input level) 0 10 dBm PER = 1%, as specified by [1] Measured in a 50 single–ended load through a balun. [1] requires –20 dBm Adjacent channel rejection + 5 MHz channel spacing 45 dB Wanted signal @ -82 dBm, adjacent modulated channel at +5 MHz, PER = 1 %, as specified by [1]. [1] requires 0 dB Adjacent channel rejection - 5 MHz channel spacing 30 dB Wanted signal @ -82 dBm, adjacent modulated channel at -5 MHz, PER = 1 %, as specified by [1]. [1] requires 0 dB Alternate channel rejection + 10 MHz channel spacing 54 dB Wanted signal @ -82 dBm, adjacent modulated channel at +10 MHz, PER = 1 %, as specified by [1] [1] requires 30 dB Alternate channel rejection - 10 MHz channel spacing 53 dB Wanted signal @ -82 dBm, adjacent modulated channel at -10 MHz, PER = 1 %, as specified by [1] [1] requires 30 dB Channel rejection ≥ + 15 MHz 62 dB ≤ - 15 MHz 62 dB Co-channel rejection Wanted signal @ -82 dBm. Undesired signal is an IEEE 802.15.4 modulated channel, stepped through all channels from 2405 to 2480 MHz. Signal level for PER = 1%. -3 dB Wanted signal @ -82 dBm. Undesired signal is an IEEE 802.15.4 modulated at the same frequency as the desired signal. Signal level for PER = 1%. -28 -28 -27 -28 dBm dBm dBm dBm Wanted signal 3 dB above the sensitivity level, CW jammer, PER = 1%. Complies with EN 300 440 class 2. -73 -58 dBm dBm Conducted measurement in a 50 single ended load. Measured according to EN 300 328, EN 300 440 class 2, FCC CFR47, Part 15 and ARIB STD-T-66 Blocking / Desensitisation +/- 5 MHz from band edge +/- 20 MHz from band edge +/- 30 MHz from band edge +/- 50 MHz from band edge Spurious emission 30 – 1000 MHz 1 – 12.75 GHz SWRS041c Page 10 of 85 CC2420 Parameter Min. Frequency error tolerance -300 Typ. Max. Unit Condition / Note 300 kHz Difference between centre frequency of the received RF signal and local oscillator frequency [1] requires 200 kHz Symbol rate error tolerance 120 ppm Difference between incoming symbol rate and the internally generated symbol rate [1] requires 80 ppm Data latency 6.4 3 s Processing delay in receiver. Time from complete transmission of SFD until complete reception of SFD, i.e. from SFD goes active on transmitter until active on receiver. Unit Condition / Note RSSI / Carrier Sense Parameter Min. Typ. Max. Carrier sense level − 77 dBm Programmable in RSSI.CCA_THR RSSI dynamic range 100 dB The range is approximately from –100 dBm to 0 dBm RSSI accuracy 6 dB See page 48 for details RSSI linearity 3 dB RSSI average time 128 s 8 symbol periods, as specified by [1] Unit Condition / Note 6.5 IF Section Parameter Min. Intermediate frequency (IF) 6.6 Typ. Max. 2 MHz Frequency Synthesizer Section Parameter Min. Crystal oscillator frequency Crystal frequency accuracy requirement Crystal operation Typ. Max. 16 - 40 40 Parallel SWRS041c Unit Condition / Note MHz See page 53 for details. ppm Including aging and temperature dependency, as specified by [1] C381 and C391 are loading capacitors, see page 53 Page 11 of 85 CC2420 Parameter Min. Typ. Max. Unit Condition / Note Crystal load capacitance 12 16 20 pF 16 pF recommended 60 Crystal ESR Crystal oscillator start-up time 1.0 ms −109 −117 −117 −117 dBc/Hz dBc/Hz dBc/Hz dBc/Hz 100 kHz Phase noise Unmodulated carrier PLL loop bandwidth PLL lock time 6.7 16 pF load At ±1 MHz offset from carrier At ±2 MHz offset from carrier At ±3 MHz offset from carrier At ±5 MHz offset from carrier 192 s The startup time from the crystal oscillator is running and RX / TX turnaround time Max. Unit Condition / Note Digital Inputs/Outputs Parameter Min. Typ. General Signal levels are referred to the voltage level at pin DVDD3.3 Logic "0" input voltage 0 0.3* DVDD V Logic "1" input voltage 0.7* DVDD DVDD V Logic "0" output voltage 0 0.4 V Output current −8 mA, 3.3 V supply voltage Logic "1" output voltage 2.5 VDD V Output current 8 mA, 3.3 V supply voltage Logic "0" input current NA −1 A Input signal equals GND Logic "1" input current NA 1 A Input signal equals VDD FIFO setup time 20 ns TX unbuffered mode, minimum time FIFO must be ready before the positive edge of FIFOP FIFO hold time 10 ns TX unbuffered mode, minimum time FIFO must be held after the positive edge of FIFOP Serial interface pins (SCLK, SI, SO and CSn) timing specification See Table 4 on page 28 SWRS041c Page 12 of 85 CC2420 6.8 Voltage Regulator Parameter Min. Typ. Max. Unit General Condition / Note Note that the internal voltage regulator can only supply CC2420 and no external circuitry. Input Voltage 2.1 3.0 3.6 V On the VREG_IN pin Output Voltage 1.7 1.8 1.9 V On the VREG_OUT pin Quiescent current 13 20 29 A No current drawn from the VREG_OUT pin. Min and max numbers include 2.1 through 3.6 V input voltage 0.3 0.6 ms Start-up time 6.9 Battery Monitor Parameter Min. Typ. Max. Unit Condition / Note Current consumption 6 30 90 A When enabled Start-up time 100 s Voltage regulator already enabled Settling time 2 s New toggle voltage programmed Step size 50 mV Hysteresis 10 mV Absolute accuracy -80 80 mV Relative accuracy -50 50 mV Max. Unit May be software calibrated for known reference voltage 6.10 Power Supply Parameter Min. Typ. Condition / Note Current drawn from VREG_IN, through voltage regulator Current consumption in different modes (see Figure 25, page 44) Voltage regulator off (OFF) Power Down mode (PD) Idle mode (IDLE) 0.02 20 426 Current Consumption, receive mode 18.8 1 SWRS041c A A A Voltage regulator off Voltage regulator on Including crystal oscillator and voltage regulator mA Page 13 of 85 CC2420 Parameter Min. Typ. Max. Unit Condition / Note mA mA mA mA mA The output power is delivered differentially to a 50 singled ended load through a balun, see also page 54. Current Consumption, transmit mode: P = -25 dBm P = -15 dBm P = -10 dBm P = −5 dBm P = 0 dBm 8.5 9.9 11 14 17.4 SWRS041c Page 14 of 85 CC2420 AVDD_CHP ATEST1 ATEST2 R_BIAS AVDD_IF1 VREG_IN VREG_OUT VREG_EN NC XOSC16_Q1 XOSC16_Q2 AVDD_XOSC16 47 46 45 44 43 42 41 40 39 38 37 Pin Assignment 48 7 VCO_GUARD 1 36 NC AVDD_VCO 2 35 DVDD_RAM AVDD_PRE 3 34 SO AVDD_RF1 4 33 SI GND 5 32 SCLK RF_P 6 31 CSn TXRX_SWITCH 7 30 FIFO RF_N 8 29 FIFOP GND 9 28 CCA AVDD_SW 10 27 SFD NC 11 26 DVDD1.8 NC 12 25 DVDD3.3 CC2420 QLP48 7x7 DGND_GUARD DGUARD DSUB_CORE 20 DSUB_PADS 19 DVDD_ADC 24 18 AVDD_ADC 23 17 NC RESETn 16 AVDD_IF2 DGND 15 AVDD_RF2 22 14 NC 21 13 AGND Exposed die attach pad Figure 1. CC2420 Pinout – Top View Pin Pin Name Pin type Pin Description - AGND Ground (analog) 1 2 3 4 5 6 VCO_GUARD AVDD_VCO AVDD_PRE AVDD_RF1 GND RF_P Power (analog) Power (analog) Power (analog) Power (analog) Ground (analog) RF I/O 7 TXRX_SWITCH Power (analog) 8 RF_N RF I/O 9 10 11 12 13 14 GND AVDD_SW NC NC NC AVDD_RF2 Ground (analog) Power (analog) Power (analog) Exposed die attach pad. Must be connected to solid ground plane Connection of guard ring for VCO (to AVDD) shielding 1.8 V Power supply for VCO 1.8 V Power supply for Prescaler 1.8 V Power supply for RF front-end Grounded pin for RF shielding Positive RF input/output signal to LNA/from PA in receive/transmit mode Common supply connection for integrated RF front-end. Must be connected to RF_P and RF_N externally through a DC path Negative RF input/output signal to LNA/from PA in receive/transmit mode Grounded pin for RF shielding 1.8 V Power supply for LNA / PA switch Not Connected Not Connected Not Connected 1.8 V Power supply for receive and transmit mixers SWRS041c Page 15 of 85 CC2420 Pin Pin Name Pin type Pin Description 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 AVDD_IF2 NC AVDD_ADC DVDD_ADC DGND_GUARD DGUARD RESETn DGND DSUB_PADS DSUB_CORE DVDD3.3 DVDD1.8 SFD CCA FIFOP Power (analog) Power (analog) Power (digital) Ground (digital) Power (digital) Digital Input Ground (digital) Ground (digital) Ground (digital) Power (digital) Power (digital) Digital output Digital output Digital output 30 FIFO Digital I/O 31 32 33 34 CSn SCLK SI SO 35 36 37 38 39 40 41 DVDD_RAM NC AVDD_XOSC16 XOSC16_Q2 XOSC16_Q1 NC VREG_EN Digital input Digital input Digital input Digital output (tristate) Power (digital) Power (analog) Analog I/O Analog I/O Digital input 42 43 44 45 46 47 48 VREG_OUT VREG_IN AVDD_IF1 R_BIAS ATEST2 ATEST1 AVDD_CHP Power output Power (analog) Power (analog) Analog output Analog I/O Analog I/O Power (analog) 1.8 V Power supply for transmit / receive IF chain Not Connected 1.8 V Power supply for analog parts of ADCs and DACs 1.8 V Power supply for digital parts of receive ADCs Ground connection for digital noise isolation 1.8 V Power supply connection for digital noise isolation Asynchronous, active low digital reset Ground connection for digital core and pads Substrate connection for digital pads Substrate connection for digital modules 3.3 V Power supply for digital I/Os 1.8 V Power supply for digital core SFD (Start of Frame Delimiter) / digital mux output CCA (Clear Channel Assessment) / digital mux output Active when number of bytes in FIFO exceeds threshold / serial RF clock output in test mode Active when data in FIFO / serial RF data input / output in test mode SPI Chip select, active low SPI Clock input, up to 10 MHz SPI Slave Input. Sampled on the positive edge of SCLK SPI Slave Output. Updated on the negative edge of SCLK. Tristate when CSn high. 1.8 V Power supply for digital RAM Not Connected 1.8 V crystal oscillator power supply 16 MHz Crystal oscillator pin 2 16 MHz Crystal oscillator pin 1 or external clock input Not Connected Voltage regulator enable, active high, held at VREG_IN voltage level when active. Note that VREG_EN is relative VREG_IN, not DVDD3.3. Voltage regulator 1.8 V power supply output Voltage regulator 2.1 to 3.6 V power supply input 1.8 V Power supply for transmit / receive IF chain External precision resistor, 43 k, 1 % Analog test I/O for prototype and production testing Analog test I/O for prototype and production testing 1.8 V Power supply for phase detector and charge pump NOTES: The exposed die attach pad must be connected to a solid ground plane as this is the main ground connection for the chip. SWRS041c Page 16 of 85 CC2420 8 Circuit Description AUTOMATIC GAIN CONTROL ADC DIGITAL DEMODULATOR ADC - Digital RSSI - Gain Control - Image Suppression - Channel Filtering - Demodulation - Frame synchronization LNA Serial voltage regulator CC2420 FREQ SYNTH 0 90 Serial microcontroller interface SmartRF CONTROL LOGIC TX/RX CONTROL DIGITAL INTERFACE WITH FIFO BUFFERS, CRC AND ENCRYPTION TX POWER CONTROL DAC Power Control PA DIGITAL MODULATOR - Data spreading - Modulation Digital and Analog test interface DAC XOSC On-chip BIAS R 16 MHz Figure 2. CC2420 simplified block diagram A simplified block diagram of CC2420 is shown in Figure 2. CC2420 features a low-IF receiver. The received RF signal is amplified by the lownoise amplifier (LNA) and down-converted in quadrature (I and Q) to the intermediate frequency (IF). At IF (2 MHz), the complex I/Q signal is filtered and amplified, and then digitized by the ADCs. Automatic gain control, final channel filtering, despreading, symbol correlation and byte synchronisation are performed digitally. When the SFD pin goes active, this indicates that a start of frame delimiter has been detected. CC2420 buffers the received data in a 128 byte receive FIFO. The user may read the FIFO through an SPI interface. CRC is verified in hardware. RSSI and correlation values are appended to the frame. CCA is available on a pin in receive mode. Serial (unbuffered) data modes are also available for test purposes. The CC2420 transmitter is based on direct up-conversion. The data is buffered in a 128 byte transmit FIFO (separate from the receive FIFO). The preamble and start of frame delimiter are generated by hardware. Each symbol (4 bits) is spread using the IEEE 802.15.4 spreading sequence to 32 chips and output to the digital-to-analog converters (DACs). An analog low pass filter passes the signal to the quadrature (I and Q) upconversion mixers. The RF signal is amplified in the power amplifier (PA) and fed to the antenna. The internal T/R switch circuitry makes the antenna interface and matching easy. The RF connection is differential. A balun may be used for single-ended antennas. The biasing of the PA and LNA is done by connecting TXRX_SWITCH to RF_P and RF_N through an external DC path. The frequency synthesizer includes a completely on-chip LC VCO and a 90 SWRS041c Page 17 of 85 CC2420 degrees phase splitter for generating the I and Q LO signals to the down-conversion mixers in receive mode and up-conversion mixers in transmit mode. The VCO operates in the frequency range 4800 – 4966 MHz, and the frequency is divided by two when split in I and Q. A crystal must be connected to XOSC16_Q1 and XOSC16_Q2 and provides the reference frequency for the synthesizer. A digital lock signal is available from the PLL. The digital baseband includes support for frame handling, address recognition, data buffering and MAC security. The 4-wire SPI serial interface is used for configuration and data buffering. An on-chip voltage regulator delivers the regulated 1.8 V supply voltage. The voltage regulator may be enabled / disabled through a separate pin. A battery monitor may optionally be used to monitor the unregulated power supply voltage. The battery monitor is configurable through the SPI interface. SWRS041c Page 18 of 85 CC2420 9 Application Circuit Few external components are required for the operation of CC2420. A typical application circuit is shown in Figure 4. The external components shown are described in Table 1 and typical values are given in Table 2. Note that most decoupling capacitors are not shown on the application circuits. For the complete reference design please refer to Texas Instrument’s web site: http://www.ti.com. 9.1 Input / output matching The RF input/output is high impedance and differential. The optimum differential load for the RF port is 95+j187 . When using an unbalanced antenna such as a monopole, a balun should be used in order to optimise performance. The balun can be implemented using low-cost discrete inductors and capacitors only or in combination with transmission lines. Figure 3 shows the balun implemented in a two-layer reference design. It consists of a half wave transmission line, C81, L61, L71 and L81. The circuit will present the optimum RF termination to CC2420 with a 50 load on the antenna connection. This circuit has improved EVM performance, sensitivity and harmonic suppression compared to the design in Figure 4. Please refer to the input/output matching section on page 54 for more details. The balun in Figure 4 consists of C61, C62, C71, C81, L61, L62 and L81, and will present the optimum RF termination to CC2420 with a 50 load on the antenna connection. A low pass filter may be added to add margin to the FCC requirement on second harmonic level. If a balanced antenna such as a folded dipole is used, the balun can be omitted. If the antenna also provides a DC path from the TXRX_SWITCH pin to the RF pins, inductors are not needed for DC bias. Figure 5 shows a suggested application circuit using a differential antenna. The antenna type is a standard folded dipole. The dipole has a virtual ground point; hence bias is provided without degradation in antenna performance. 9.2 Bias resistor The bias resistor R451 is used to set an accurate bias current. 9.3 Crystal An external crystal with two loading capacitors (C381 and C391) is used for the crystal oscillator. See page 53 for details. 9.4 Voltage regulator The on chip voltage regulator supplies all 1.8 V power supply inputs. C42 is required for stability of the regulator. A series resistor may be used to comply with the ESR requirement. 9.5 Power supply decoupling and filtering Proper power supply decoupling must be used for optimum performance. The placement and size of the decoupling capacitors and the power supply filtering are very important to achieve the best performance in an application. Texas Instruments provides a compact reference design that should be followed very closely.. SWRS041c Page 19 of 85 CC2420 Ref Description C42 Voltage regulator load capacitance C61 Balun and match C62 DC block to antenna and match C71 Front-end bias decoupling and match C81 Balun and match C381 16MHz crystal load capacitor, see page 53 C391 16MHz crystal load capacitor, see page 53 L61 DC bias and match L62 DC bias and match L71 DC bias and match L81 Balun and match R451 Precision resistor for current reference generator XTAL 16MHz crystal, see page 53 Table 1. Overview of external components 3.3 V Power supply C391 C381 C42 R451 C81 L81 L71 XOSC16_Q2 38 AVDD_XOSC16 37 NC 40 VREG_EN 41 VREG_IN 43 XOSC16_Q1 39 NC 36 2 AVDD_VCO DVDD_RAM 35 3 AVDD_PRE SO 34 4 AVDD_RF1 5 GND 6 RF_P 7 TXRX_SWITCH 8 RF_N 9 GND SI 33 CC2420 SCLK 32 QLP48 RF 7x7 L61 CSn 31 FIFO 30 Transceiver FIFOP 29 CCA 28 10 AVDD_SW SFD 27 11 NC DVDD1.8 26 DSUB_CORE 24 DSUB_PADS 23 DGND 22 RESETn 21 DGUARD 20 DGND_GUARD 19 DVDD_ADC 18 NC 16 AVDD_ADC 17 AVDD_IF2 15 NC 13 AVDD_RF2 14 12 NC Digital Interface Antenna (50 Ohm) VREG_OUT 42 1 VCO_GUARD AVDD_IF1 44 ATEST2 46 R_BIAS 45 ATEST1 47 AVDD_CHP 48 XTAL DVDD3.3 25 Figure 3. Typical application circuit with transmission line balun for single-ended operation SWRS041c Page 20 of 85 CC2420 3.3 V Power supply C391 C381 R451 C62 C71 L81 C81 L61 XOSC16_Q2 38 AVDD_XOSC16 37 XOSC16_Q1 39 NC 40 VREG_EN 41 VREG_OUT 42 NC 36 2 AVDD_VCO DVDD_RAM 35 3 AVDD_PRE SO 34 4 AVDD_RF1 SI 33 5 GND 6 RF_P C61 L62 XTAL CC2420 7 TXRX_SWITCH 8 RF_N 9 GND SCLK 32 QLP48 RF 7x7 CSn 31 FIFO 30 Transceiver Digital Interface Antenna (50 Ohm) VREG_IN 43 R_BIAS 45 1 VCO_GUARD AVDD_IF1 44 ATEST2 46 ATEST1 47 AVDD_CHP 48 C42 FIFOP 29 CCA 28 10 AVDD_SW SFD 27 11 NC DVDD1.8 26 DSUB_CORE 24 DGND 22 DSUB_PADS 23 RESETn 21 DGUARD 20 DVDD_ADC 18 DGND_GUARD 19 NC 16 AVDD_ADC 17 AVDD_IF2 15 NC 13 AVDD_RF2 14 12 NC DVDD3.3 25 Figure 4. Typical application circuit with discrete balun for single-ended operation SWRS041c Page 21 of 85 CC2420 3.3 V Power supply C391 C381 R451 L61 AVDD_XOSC16 37 XOSC16_Q2 38 XOSC16_Q1 39 NC 40 VREG_EN 41 VREG_IN 43 XTAL NC 36 2 AVDD_VCO DVDD_RAM 35 3 AVDD_PRE SO 34 4 AVDD_RF1 5 GND 6 RF_P CC2420 7 TXRX_SWITCH 8 RF_N 9 GND L71 SI 33 SCLK 32 QLP48 RF 7x7 CSn 31 FIFO 30 Transceiver Digital Interface Folded dipole antenna VREG_OUT 42 1 VCO_GUARD AVDD_IF1 44 R_BIAS 45 ATEST2 46 ATEST1 47 AVDD_CHP 48 C42 FIFOP 29 CCA 28 10 AVDD_SW SFD 27 11 NC DVDD1.8 26 DSUB_CORE 24 DGND 22 DSUB_PADS 23 DGUARD 20 RESETn 21 DGND_GUARD 19 DVDD_ADC 18 AVDD_ADC 17 NC 16 AVDD_IF2 15 NC 13 AVDD_RF2 14 12 NC DVDD3.3 25 Figure 5. Suggested application circuit with differential antenna (folded dipole) SWRS041c Page 22 of 85 CC2420 Item Single ended output, transmission line balun Single ended discrete balun output, Differential antenna C42 10 μF, 0.5 < ESR < 5 10 μF, 0.5 < ESR < 5 10 μF, 0.5 < ESR < 5 C61 Not used 0.5 pF, +/- 0.25pF, NP0, 0402 Not used C62 Not used 5.6 pF, +/- 0.25pF, NP0, 0402 Not used C71 Not used 5.6 pF, 10%, X5R, 0402 Not used C81 5.6 pF, +/- 0.25pF, NP0, 0402 0.5 pF, +/- 0.25pF, NP0, 0402 Not used C381 27 pF, 5%, NP0, 0402 27 pF, 5%, NP0, 0402 27 pF, 5%, NP0, 0402 C391 27 pF, 5%, NP0, 0402 27 pF, 5%, NP0, 0402 27 pF, 5%, NP0, 0402 L61 8.2 nH, 5%, Monolithic/multilayer, 0402 7.5 nH, 5%, Monolithic/multilayer, 0402 27 nH, 5%, Monolithic/multilayer, 0402 L62 Not used 5.6 nH, 5%, Monolithic/multilayer, 0402 Not used L71 22 nH, 5%, Monolithic/multilayer, 0402 Not used 12 nH, 5%, Monolithic/multilayer, 0402 L81 1.8 nH, +/- 0.3nH, Monolithic/multilayer, 0402 7.5 nH, 5%, Monolithic/multilayer, 0402 Not used R451 43 k, 1%, 0402 43 k, 1%, 0402 43 k, 1%, 0402 XTAL 16 MHz crystal, 16 pF load (CL), ESR < 60 16 MHz crystal, 16 pF load (CL), ESR < 60 16 MHz crystal, 16 pF load (CL), ESR < 60 Table 2. Bill of materials for the application circuits SWRS041c Page 23 of 85 CC2420 10 IEEE 802.15.4 Modulation Format This section is meant as an introduction to the 2.4 GHz direct sequence spread spectrum (DSSS) RF modulation format defined in IEEE 802.15.4. For a complete description, please refer to [1]. least significant byte is transmitted first, except for security related fields where the most significant byte it transmitted first. Each symbol is mapped to one out of 16 pseudo-random sequences, 32 chips each. The symbol to chip mapping is shown in Table 3. The chip sequence is then transmitted at 2 MChips/s, with the least significant chip (C0) transmitted first for each symbol. The modulation and spreading functions are illustrated at block level in Figure 6 [1]. Each byte is divided into two symbols, 4 bits each. The least significant symbol is transmitted first. For multi-byte fields, the Transmitted bit-stream (LSB first) Bit-toSymbol Symbolto-Chip O-QPSK Modulator Modulated Signal Figure 6. Modulation and spreading functions [1] Symbol Chip sequence (C0, C1, C2, … , C31) 0 11011001110000110101001000101110 1 11101101100111000011010100100010 2 00101110110110011100001101010010 3 00100010111011011001110000110101 4 01010010001011101101100111000011 5 00110101001000101110110110011100 6 11000011010100100010111011011001 7 10011100001101010010001011101101 8 10001100100101100000011101111011 9 10111000110010010110000001110111 10 01111011100011001001011000000111 11 01110111101110001100100101100000 12 00000111011110111000110010010110 13 01100000011101111011100011001001 14 10010110000001110111101110001100 15 11001001011000000111011110111000 Table 3. IEEE 802.15.4 symbol-to-chip mapping [1] The modulation format is Offset – Quadrature Phase Shift Keying (O-QPSK) with half-sine chip shaping. This is equivalent to MSK modulation. Each chip is shaped as a half-sine, transmitted alternately in the I and Q channels with one half chip period offset. This is illustrated for the zero-symbol in Figure 7. SWRS041c Page 24 of 85 CC2420 TC I-phase 1 Q-phase 0 1 0 1 1 0 1 1 0 1 1 0 0 0 0 1 0 1 1 0 1 0 0 0 1 0 1 1 0 1 0 2TC Figure 7. I / Q Phases when transmitting a zero-symbol chip sequence, TC = 0.5 μs 11 Configuration Overview CC2420 can be configured to achieve the best performance for different applications. Through the programmable configuration registers the following key parameters can be programmed: Power-down / power-up mode Crystal oscillator power-up / power down Clear Channel Assessment mode Packet handling hardware support Encryption / Authentication modes SWRS041c Page 25 of 85 Receive / transmit mode RF channel selection RF output power CC2420 12 Evaluation Software Texas Instruments (TI) provides users of CC2420 with a software program, ® SmartRF Studio (Windows interface) which may be used for radio performance and functionality evaluation. SmartRF® Studio can be downloaded from TI’s web page: http://www.ti.com. Figure 8 shows the user interface of the CC2420 configuration software. Figure 8. SmartRF Studio user interface SWRS041c Page 26 of 85 CC2420 13 4-wire Serial Configuration and Data Interface CC2420 is configured via a simple 4-wire SPI-compatible interface (pins SI, SO, SCLK and CSn) where CC2420 is the slave. This interface is also used to read and write buffered data (see page 39). All address and data transfer on the SPI interface is done most significant bit first. 13.1 Pin configuration The digital inputs SCLK, SI and CSn are high-impedance inputs (no internal pull-up) and should have external pull-ups if not driven. SO is high-impedance when CSn is high. An external pull-up should be used at SO to prevent floating input at microcontroller. Unused I/O pins on the MCU can be set to outputs with a fixed ‘0’ level to avoid leakage currents. 13.2 Register access There are 33 16-bit configuration and status registers, 15 command strobe registers, and two 8-bit registers to access the separate transmit and receive FIFOs. Each of the 50 registers is addressed by a 6-bit address. The RAM/Register bit (bit 7) must be cleared for register access. The Read/Write bit (bit 6) selects a read or a write operation and makes up the 8-bit address field together with the 6-bit address. In each register read or write cycle, 24 bits are sent on the SI-line. The CSn pin (Chip Select, active low) must be kept low during this transfer. The bit to be sent first is the RAM/Register bit (set to 0 for register access), followed by the R/W bit (0 for write, 1 for read). The following 6 bits are the address-bits (A5:0). A5 is the most significant bit of the address and is sent first. The 16 data-bits are then transferred (D15:0), also MSB first. See Figure 9 for an illustration. The configuration registers can also be read by the microcontroller via the same configuration interface. The R/W bit must be set high to initiate the data read-back. CC2420 then returns the data from the addressed register on the 16 clock cycles following the register address. The SO pin is used as the data output and must be configured as an input by the microcontroller. The timing for the programming is also shown in Figure 9 with reference to Table 4. The clocking of the data on SI into the CC2420 is done on the positive edge of SCLK. When the last bit, D0, of the 16 data-bits has been written, the data word is loaded in the internal configuration register. Multiple registers may be written without releasing CSn, as described in the Multiple SPI access section on page 31. The register data will be retained during power down mode, but not when the power-supply is turned off (e.g. by disabling the voltage regulator using the VREG_EN pin). The registers can be programmed in any order. SWRS041c Page 27 of 85 CC2420 tsp tch tcl thd tsd tns SCLK CSn Write to register / RXFIFO: SI 0 0 A5 A4 A3 A2 A1 A0 SO S7 S6 S5 S4 S3 S2 S1 S0 X DW15 DW14 DW13 DW12 DW11 DW10 DW9 DW8 X DW7 DW6 DW5 DW4 DW3 DW2 DW1 DW0 X DW7 DW6 DW5 DW4 DW3 DW2 DW1 DW0 X S6 S5 S4 S3 S2 S1 S0 DR6 DR5 DR4 DR3 DR2 DR1 DR0 X Write to TXFIFO: SI 0 0 A5 A4 A3 A2 A1 A0 SO S7 S6 S5 S4 S3 S2 S1 S0 X DW7 S7 DW6 DW5 DW4 DW3 DW2 DW1 DW0 S6 S5 S4 S3 S2 S1 S0 X S7 DR9 DR8 DR7 X X S7 Read from register / RXFIFO: SI 0 1 A5 A4 A3 A2 A1 A0 SO S7 S6 S5 S4 S3 S2 S1 S0 X DR15 DR14 DR13 DR12 DR11 DR10 DR15 Read and write one byte to RAM: (multiple read / writes also possible) SI 1 A6 A5 A4 A3 A2 A1 A0 SO S7 S6 S5 S4 S3 S2 S1 S0 X B1 B0 0 X X X X X DW6 DW5 DW4 DW3 DW2 DW1 DW0 X DR7 DW7 DR6 DR5 DR4 DR3 DR2 DR1 DR0 DR7 DR7 DR6 DR5 DR4 DR3 DR2 DR1 DR0 DR7 Read one byte from RAM: (multiple reads also possible) SI 1 A6 A5 A4 A3 A2 A1 A0 SO S7 S6 S5 S4 S3 S2 S1 S0 X B1 B0 1 X X X X X X X Figure 9. SPI timing diagram Parameter Symbol Min Max Units 10 MHz Conditions SCLK, clock frequency FSCLK SCLK low pulse duration tcl 25 ns The minimum time SCLK must be low. SCLK high pulse duration tch 25 ns The minimum time SCLK must be high. CSn setup time tsp 25 ns The minimum time CSn must be low before the first positive edge of SCLK. CSn hold time tns 25 ns The minimum time CSn must be held low after the last negative edge of SCLK. SI setup time tsd 25 ns The minimum time data on SI must be ready before the positive edge of SCLK. SI hold time thd 25 ns The minimum time data must be held at SI, after the positive edge of SCLK. Rise time trise 100 ns The maximum rise time for SCLK and CSn Fall time tfall 100 ns The maximum fall time for SCLK and CSn Note: The set-up- and hold-times refer to 50% of VDD. Table 4. SPI timing specification 13.3 Status byte pin. The status byte contains 6 status bits which are described in Table 5. During transfer of the register access byte, command strobes, the first RAM address byte and data transfer to the TXFIFO, the CC2420 status byte is returned on the SO Issuing a SNOP (no operation) command strobe may be used to read the status byte. It may also be read during access to SWRS041c Page 28 of 85 CC2420 chip functions such as register or FIFO access. Bit # Name Description 7 - Reserved, ignore value 6 XOSC16M_STABLE Indicates whether the 16 MHz oscillator is running or not 0 : The 16 MHz crystal oscillator is not running 1 : The 16 MHz crystal oscillator is running 5 TX_UNDERFLOW Indicates whether an FIFO underflow has occurred during transmission. Must be cleared manually with a SFLUSHTX command strobe. 0 : No underflow has occurred 1 : An underflow has occurred 4 ENC_BUSY Indicates whether the encryption module is busy 0 : Encryption module is idle 1 : Encryption module is busy 3 TX_ACTIVE Indicates whether RF transmission is active 0 : RF Transmission is idle 1 : RF Transmission is active 2 LOCK Indicates whether the frequency synthesizer PLL is in lock or not 0 : The PLL is out of lock 1 : The PLL is in lock 1 RSSI_VALID Indicates whether the RSSI value is valid or not. 0 : The RSSI value is not valid 1 : The RSSI value is valid, always true when reception has been enabled at least 8 symbol periods (128 us) 0 - Reserved, ignore value Table 5. Status byte returned during address transfer and TXFIFO writing 13.4 Command strobes Command strobes may be viewed as single byte instructions to CC2420. By addressing a command strobe register internal sequences will be started. These commands must be used to enable the crystal oscillator, enable receive mode, start decryption etc. All 15 command strobes are listed in Table 11 on page 62. When the crystal oscillator is disabled (Power Down state in Figure 25 on page 44), only the SXOSCON command strobe may be used. All other command strobes will be ignored and will have no effect. The crystal oscillator must stabilise (see the XOSC16M_STABLE status bit in Table 5) before other command strobes are accepted. The command strobe register is accessed in the same way as for a register write operation, but no data is transferred. That is, only the RAM/Register bit (set to 0), R/W bit (set to 0) and the 6 address bits (in the range 0x00 through 0x0E) are written. A command strobe may be followed by any other SPI access without pulling CSn high, and is executed on the last falling edge on SCLK. 13.5 RAM access The internal 368 byte RAM may be accessed through the SPI interface. Single or multiple bytes may be read or written sending the address part (2 bytes) only once. The address is then automatically incremented by the CC2420 hardware for each new byte. Data is read and written one byte at a time, unlike register access where 2 bytes are always required after each address byte. The crystal oscillator must be running when accessing the RAM. The RAM/Register bit must be set high to enable RAM access. The 9 bit RAM SWRS041c Page 29 of 85 CC2420 address consists of two parts, B1:0 (MSB) selecting one of the three memory banks and A6:0 (LSB) selecting the address within the selected bank. The RAM is divided into three memory banks: TXFIFO (bank 0), RXFIFO (bank 1) and security (bank 2). The FIFO banks are 128 bytes each, while the security bank is 112 bytes. For RAM read, the selected byte(s) are output on the SO pin directly after the second address byte. See Figure 10 for an illustration on how multiple RAM bytes may be read or written in one operation. The RAM memory space is shown in Table 6. The lower 256 bytes are used to store FIFO data. Note that RAM access should never be used for FIFO write operations because the FIFO counter will not be updated. Use RXFIFO and TXFIFO access instead as described in section FIFO access. A6:0 is transmitted directly after the RAM/Register bit as shown in Figure 9. For RAM access, a second byte is also required before the data transfer. This byte contains B1:0 in bits 7 and 6, followed by the R/W bit (0 for read+write, 1 for read). Bits 4 through 0 are don’t care as shown in Figure 9. As with register data, data stored in RAM will be retained during power down mode, but not when the power-supply is turned off (e.g. by disabling the voltage regulator using the VREG_EN pin). For RAM write, data to be written must be input on the SI pin directly after the second address byte. RAM data read is output on the SO pin simultaneously, but may be ignored by the user if only writing is of interest. CSn: Command strobe: ADDR Multiple command strobes: ADDR ADDR ADDR Read or write a whole register (16 bit): ADDR DATA8MSB DATA8LSB Read 8 MSB of a register: ADDR DATA8MSB ADDR DATA8MSB DATA8LSB ADDR DATA8MSB ... ADDRFIFO DATAbyte0 DATAbyte1 DATAbyte2 DATAbyte3 ... DATAbyte n-3 DATAbyte n-2 DATAbyte n-1 ADDRLRAM ADDRHRAM DATAADDR DATAADDR+1 DATAADDR+2 ... DATAADDR+n Multiple register read or write Read or write n bytes from/to RF FIFO: Read or write n bytes from/to RAM: Note: ... ... ADDR ADDR ADDR DATA8MSB DATA8LSB FIFO and RAM access must be terminated with setting the CSn pin high. Command strobes and register access may be followed by any other access, since they are completed on the last negative edge on SCLK. They may however also be terminated with setting CSn high, if desirable, e.g. for reading only 8 bits from a configuration register. Figure 10. Configuration registers write and read operations via SPI SWRS041c Page 30 of 85 CC2420 Address Byte Ordering Name Description 0x16F – 0x16C - - Not used 0x16B – 0x16A MSB LSB SHORTADR 16-bit Short address, used for address recognition. 0x169 – 0x168 MSB LSB PANID 16-bit PAN identifier, used for address recognition. 0x167 – 0x160 MSB LSB IEEEADR 64-bit IEEE address of current node, used for address recognition. 0x15F – 0x150 MSB LSB CBCSTATE Temporary storage for CBC-MAC calculations 0x14F – 0x140 MSB (Flags) LSB TXNONCE / TXCTR Transmitter nonce for in-line authentication and transmitter counter for in-line encryption. 0x13F – 0x130 MSB LSB KEY1 Encryption key 1 0x12F – 0x120 MSB LSB SABUF Stand-alone encryption buffer, for plaintext input and ciphertext output 0x11F – 0x110 MSB (Flags) LSB RXNONCE / RXCTR Receiver nonce for in-line authentication or receiver counter for in-line decryption. 0x10F – 0x100 MSB LSB KEY0 Encryption key 0 0x0FF – 0x080 MSB LSB RXFIFO 128 bytes receive FIFO 0x07F – 0x000 MSB LSB TXFIFO 128 bytes transmit FIFO Table 6. CC2420 RAM Memory Space 13.6 FIFO access The TXFIFO and RXFIFO may be accessed through the TXFIFO (0x3E) and RXFIFO (0x3F) registers. The TXFIFO is write only, but may be read back using RAM access as described in the previous section. Data is read and written one byte at a time, as with RAM access. The RXFIFO is both writeable and readable. Writing to the RXFIFO should however only be done for debugging or for using the RXFIFO for security operations (decryption / authentication). The crystal oscillator must be running when accessing the FIFOs. When writing to the TXFIFO, the status byte (see Table 5) is output for each new data byte on SO, as shown in Figure 9. This could be used to detect TXFIFO underflow (see section RF Data Buffering section on page 39) while writing data to the TXFIFO. Multiple FIFO bytes may be accessed in one operation, as with the RAM access. FIFO access can only be terminated by setting the CSn pin high once it has been started. The FIFO and FIFOP pins also provide additional information on the data in the receive FIFO, as will be described in the Microcontroller Interface and Pin Description section on page 32. Note that the FIFO and FIFOP pins only apply to the RXFIFO. The TXFIFO has its underflow flag in the status byte. The TXFIFO may be flushed by issuing a SFLUSHTX command strobe. Similarly, a SFLUSHRX command strobe will flush the receive FIFO. 13.7 Multiple SPI access Register access, command strobes, FIFO access and RAM access may be issued continuously without setting CSn high. E.g. the user may issue a command strobe, a register write and writing 3 bytes to the TXFIFO in one operation, as illustrated in Figure 11. The only exception is that FIFO and RAM access must be terminated by setting CSn high. SWRS041c Page 31 of 85 CC2420 CSn SI ADDR ADDR - - SO Status Status DATA8MSB DATA8LSB Command Strobe ADDRTXFIFO DATAADDR DATAADDR+1 DATAADDR+2 Status Status Register Read Status Status TXFIFO Write Figure 11. Multiple SPI Access Example 14 Microcontroller Interface and Pin Description When used in a typical system, CC2420 will interface to a microcontroller. This microcontroller must be able to: Program CC2420 into different modes, read and write buffered data, and read back status information via the 4-wire SPI-bus configuration interface (SI, SO, SCLK and CSn). Interface to the receive and transmit FIFOs using the FIFO and FIFOP status pins. Interface to the CCA pin for clear channel assessment. Interface to the SFD pin for timing information (particularly for beaconing networks). microcontroller uses 4 I/O pins for the SPI configuration interface (SI, SO, SCLK and CSn). SO should be connected to an input at the microcontroller. SI, SCLK and CSn must be microcontroller outputs. Preferably the microcontroller should have a hardware SPI interface. The microcontroller pins connected to SI, SO and SCLK can be shared with other SPI-interface devices. SO is a high impedance output as long as CSn is not activated (active low). CSn should have an external pull-up resistor or be set to a high level when the voltage regulator is turned off in order to prevent the input from floating. SI and SCLK should be set to a defined level to prevent the inputs from floating. 14.1 Configuration interface A CC2420 to microcontroller interface example is shown in Figure 12. The C CC2420 FIFO GIO0 FIFOP Interrupt CCA GIO1 SFD Timer Capture CSn SI SO SCLK GIO2 MOSI MISO SCLK Figure 12. Microcontroller interface example SWRS041c Page 32 of 85 CC2420 14.2 Receive mode In receive mode, the SFD pin goes active after the start of frame delimiter (SFD) field has been completely received. If address recognition is disabled or is successful, the SFD pin goes inactive again only after the last byte of the MPDU has been received. If the received frame fails address recognition, the SFD pin goes inactive immediately. This is illustrated in Figure 13. The FIFO pin is active when there are one or more data bytes in the RXFIFO. The first byte to be stored in the RXFIFO is the length field of the received frame, i.e. the FIFO pin goes active when the length field is written to the RXFIFO. The FIFO pin then remains active until the RXFIFO is empty. If a previously received frame is completely or partially inside the RXFIFO, the FIFO pin will remain active until the RXFIFO is empty. The FIFOP pin is active when the number of unread bytes in the RXFIFO exceeds the threshold programmed into IOCFG0.FIFOP_THR. When address recognition is enabled the FIFOP pin will remain inactive until the incoming frame passes address recognition, even if the number of bytes in the RXFIFO exceeds the programmed threshold. The FIFOP pin will also go active when the last byte of a new packet is received, even if the threshold is not exceeded. If so, the FIFOP pin will go inactive once one byte has been read out of the RXFIFO. When address recognition is enabled, data should not be read out of the RXFIFO before the address is completely received, since the frame may be automatically flushed by CC2420 if it fails address recognition. This may be handled by using the FIFOP pin, since this pin does not go active until the frame passes address recognition. Figure 14 shows an example of pin activity when reading a packet from the RXFIFO. In this example, the packet size is 8 bytes, IOCFG0.FIFOP_THR = 3 and MODEMCTRL0.AUTOCRC is set. The length will be 8 bytes, RSSI will contain the average RSSI level during reception of the packet and FCS/corr contains information of FCS check result and the correlation levels. 14.3 RXFIFO overflow The RXFIFO can only contain a maximum of 128 bytes at a given time. This may be divided between multiple frames, as long as the total number of bytes is 128 or less. If an overflow occurs in the RXFIFO, this is signalled to the microcontroller by making the FIFO pin go inactive while the FIFOP pin is active. Data already in the RXFIFO will not be affected by the overflow, i.e. frames already received may be read out. A SFLUSHRX command strobe is required after an RXFIFO overflow to enable reception of new data. Note that the SFLUSHRX command strobe should be issued twice to ensure that the SFD pin goes back to its inactive state. For security enabled frames, the MAC layer must read the source address of the received frame before it can decide which key to use to decrypt or authenticate. This data must therefore not be overwritten even if it has been read out of the RXFIFO by the microcontroller. If the SECCTRL0.RXFIFO_PROTECTION control bit is set, CC2420 also protects the frame header of security enabled frames until decryption has been performed. If no MAC security is used or if it is implemented outside the CC2420, this bit may be cleared to achieve optimal use of the RXFIFO. SWRS041c Page 33 of 85 CC2420 on ed iv ce re d e te ct by te th de D ng e F L S Data received over RF Address recognition OK iti gn co re s d es te dr le Ad omp c U d PD eive t M rec s La yte b Preamble SFD Length MAC Protocol Data Unit (MPDU) with correct address Preamble SFD Length MAC Protocol Data Unit (MPDU) with wrong address SFD Pin FIFO Pin FIFOP Pin, if threshold higher than frame length FIFOP Pin, if threshold lower than frame length Data received over RF Address recognition fails SFD Pin FIFO Pin FIFOP Pin Figure 13. Pin activity examples during receive n he w te w by o l st es la go t of FO ou FI ad s re tart s gh f hi r o ns be HR i a m um _T re n P P as IFO FO ng F FI s lo s > a yte b SCLK SFD CSn SI ADDRTXFIFO - - - - - - - - - SO Status Length PSDU0 PSDU1 PSDU2 PSDU3 PSDU4 PSDU5 RSSI FCS/Corr FIFOP FIFO Figure 14. Example of pin activity when reading RXFIFO. 14.4 Transmit mode During transmit the FIFO and FIFOP pins are still only related to the RXFIFO. The SFD pin is however active during transmission of a data frame, as shown in Figure 15. The SFD pin goes active when the SFD field has been completely transmitted. It goes inactive again when the complete MPDU (as defined by the length field) has been transmitted or if an underflow is detected. See the RF Data Buffering section on page 39 for more information on TXFIFO underflow. As can be seen from comparing Figure 13 and Figure 15, the SFD pin behaves very similarly during reception and transmission of a data frame. If the SFD pins of the transmitter and the receiver are compared during the transmission of a data frame, a small delay of approximately 2 μs can be seen because of bandwidth limitations in both the transmitter and the receiver. SWRS041c Page 34 of 85 CC2420 m d an m co d U itte PD sm w o M n l f st tra er La yte nd b Xu T ed n N XO e ST trob s Data transmitted over RF itt sm D tra SF Preamble SFD Length MAC Protocol Data Unit (MPDU) SFD Pin 12 symbol periods Automatically generated preamble and SFD Data fetched from TXFIFO CRC generated by CC2420 Figure 15. Pin activity example during transmit 14.5 General control and status pins In receive mode, the FIFOP pin can be used to interrupt the microcontroller when a threshold has been exceeded or a complete frame has been received. This pin should then be connected to a microcontroller interrupt pin. In receive mode, the FIFO pin can be used to detect if there is data at all in the receive FIFO. The SFD pin can be used to extract the timing information of transmitted and received data frames. The SFD pin will go active when a start of frame delimiter has been completely detected / transmitted. The SFD pin should preferably be connected to a timer capture pin on the microcontroller. For debug purposes, the SFD and CCA pins can be used to monitor several status signals as selected by the IOCFG1 register. See Table 12 and Table 13 for available signals. The polarity of FIFO, FIFOP, SFD and CCA can be controlled by the IOCFG0 register (address 0x1C). 15 Demodulator, Symbol Synchroniser and Data Decision The block diagram for the CC2420 demodulator is shown in Figure 16. Channel filtering and frequency offset compensation is performed digitally. The signal level in the channel is estimated to generate the RSSI level (see the RSSI / Energy Detection section on page 48 for more information). Data filtering is also included for enhanced performance. With the ±40 ppm frequency accuracy requirement from [1], a compliant receiver must be able to compensate for up to 80 ppm or 200 kHz. The CC2420 demodulator tolerates up to 300 kHz offset without significant degradation of the receiver performance. Soft decision is used at the chip level, i.e. the demodulator does not make a decision for each chip, only for each received symbol. De-spreading is performed using over sampled symbol correlators. Symbol synchronisation is achieved by a continuous start of frame delimiter (SFD) search. When a SFD is detected, data is written to the RXFIFO and may be read out by the microcontroller at a lower bit rate than the 250 kbps generated by the receiver. The CC2420 demodulator also handles symbol rate errors in excess of 120 ppm without performance degradation. Resynchronisation is performed continuously to adjust for error in the incoming symbol rate. The RXCTRL1.RXBPF_LOCUR control bit should be written to 1. The MDMCTRL1.CORR_THR control bits are by default set to 20 defining the threshold for detecting IEEE 802.15.4 start of frame delimiters. SWRS041c Page 35 of 85 or CC2420 I / Q Analog IF signal Digital IF Channel Filtering ADC Frequency Offset Compensation RSSI Generator Digital Data Filtering Symbol Correlators and Synchronisation Data Symbol Output Average Correlation Value (may be used for LQI) RSSI Figure 16. Demodulator Simplified Block Diagram 16 Frame Format CC2420 has hardware support for parts of the IEEE 802.15.4 frame format. This section gives a brief summary to the IEEE 802.15.4 frame format, and describes how CC2420 is set up to comply with this. Figure 17 [1] shows a schematic view of the IEEE 802.15.4 frame format. Similar figures describing specific frame formats (data frames, beacon frames, acknowledgment frames and MAC command frames) are included in [1]. Bytes: 1 0 to 20 2 Frame Data Address Control Field Sequence Information (FCF) Number MAC Header (MHR) MAC Layer Bytes: PHY Layer 1 1 Start of frame Frame Delimiter Length (SFD) Synchronisation Header PHY Header (SHR) (PHR) n Frame payload MAC Payload 2 Frame Check Sequence (FCS) MAC Footer (MFR) 5 + (0 to 20) + n MAC Protocol Data Unit (MPDU) PHY Service Data Unit (PSDU) 4 Preamble Sequence 11 + (0 to 20) + n PHY Protocol Data Unit (PPDU) Figure 17. Schematic view of the IEEE 802.15.4 Frame Format [1] 16.1 Synchronisation header The synchronisation header (SHR) consists of the preamble sequence followed by the start of frame delimiter (SFD). In [1], the preamble sequence is defined to be 4 bytes of 0x00. The SFD is one byte, set to 0xA7. In CC2420, the preamble length and SFD is configurable. The default values are compliant with [1]. Changing these values will make the system non-compliant to IEEE 802.15.4. A synchronisation header is always transmitted first in all transmit modes. The preamble sequence length can be set by MDMCTRL0.PREAMBLE_LENGTH, while the SFD is programmed in the SYNCWORD register. SYNCWORD is 2 bytes long, which gives the user some extra flexibility as described below. Figure 18 shows how the CC2420 synchronisation header relates to the IEEE 802.15.4 specification. The programmable preamble length only applies to transmission, it does not affect receive mode. The preamble length should not be set shorter than the default value. Note that 2 of the 8 zero-symbols in the preamble sequence required by [1] are included in the SYNCWORD register so that the CC2420 preamble sequence is only 6 symbols long for compliance with [1]. Two SWRS041c Page 36 of 85 CC2420 A. If SYNCWORD = 0xA70F, CC2420 will require the incoming symbol sequence of (from left to right) 0 0 7 A. If SYNCWORD = 0xA700, CC2420 will require the incoming symbol sequence of (from left to right) 0 0 0 7 A. additional zero symbols in SYNCWORD make CC2420 compliant with [1]. In reception, CC2420 synchronises to received zero-symbols and searches for the SFD sequence defined by the SYNCWORD register. The least significant symbols in SYNCWORD set to 0xF will be ignored, while symbols different from 0xF will be required for synchronisation. The default setting of 0xA70F thereby requires one additional zero-symbol for synchronisation. This will reduce the number of false frames detected due to noise. In receive mode CC2420 uses the preamble sequence for symbol synchronisation and frequency offset adjustments. The SFD is used for byte synchronisation, and is not part of the data stored in the receive buffer (RXFIFO). The following illustrates how the programmed synch word is interpreted during reception by CC2420: If SYNCWORD = 0xA7FF, CC2420 will require the incoming symbol sequence of (from left to right) 0 7 Synchronisation Header Preamble IEEE 802.15.4 CC2420 0 0 0 0 SFD 0 0 2·(PREAMBLE_LENGTH + 1) zero symbols 0 0 7 A SW0 SW1 SW2 SW3 Each box corresponds to 4 bits. Hence the preamble corresponds to 8 x 4 ''0' s or 4 bytes with the value 0. SW0 = SYNCWORD[3:0] if different from 'F', else '0' SW1 = SYNCWORD[7:4] if different from 'F', else '0' SW2 = SYNCWORD[11:8] if different from 'F', else '0' SW3 = SYNCWORD[15:12] if different from 'F', else '0' Figure 18. Transmitted Synchronisation Header 16.2 Length field The frame length field shown in Figure 17 defines the number of bytes in the MPDU. Note that the length field does not include the length field itself. It does however include the FCS (Frame Check Sequence), even if this is inserted automatically by CC2420 hardware. It also includes the MIC if authentication is used. The length field is 7 bits and has a maximum value of 127. The most significant bit in the length field is reserved [1], and should be set to zero. CC2420 uses the length field both for transmission and reception, so this field must always be included. In transmit mode, the length field is used for underflow detection, as described in the FIFO access section on page 31. 16.3 MAC protocol data unit The FCF, data sequence number and address information follows the length field as shown in Figure 17. Together with the MAC data payload and Frame Check Sequence, they form the MAC Protocol Data Unit (MPDU). The format of the FCF is shown in Figure 19. Please refer to [1] for details. SWRS041c Page 37 of 85 CC2420 CC2420 There is no hardware support for the data sequence number, this field must be inserted and verified by software. includes hardware address recognition, as described in the Address Recognition section on page 41. Bits: 0-2 3 4 5 6 7-9 10-11 12-13 14-15 Frame Type Security Enabled Frame Pending Acknowledge request Intra PAN Reserved Destination addressing mode Reserved Source addressing mode Figure 19. Format of the Frame Control Field (FCF) [1] interested in the correctness of the FCS, not the FCS sequence itself. The FCS sequence itself is therefore not written to the RXFIFO during receive. 16.4 Frame check sequence A 2-byte frame check sequence (FCS) follows the last MAC payload byte as shown in Figure 17. The FCS is calculated over the MPDU, i.e. the length field is not part of the FCS. This field is automatically generated and verified by hardware when the MODEMCTRL0.AUTOCRC control bit is set. It is recommended to always have this enabled, except possibly for debug purposes. If cleared, CRC generation and verification must be performed by software. Instead, when MODEMCTRL0.AUTOCRC is set the two FCS bytes are replaced by the RSSI value, average correlation value (used for LQI) and CRC OK/not OK. This is illustrated in Figure 21. The first FCS byte is replaced by the 8-bit RSSI value. This RSSI value is measured over the first 8 symbols following the SFD. See the RSSI section on page 48 for details. The FCS polynomial is [1]: 16 12 5 The 7 least significant bits in the last FCS byte are replaced by the average correlation value of the 8 first symbols of the received PHY header (length field) and PHY Service Data Unit (PSDU). This correlation value may be used as a basis for calculating the LQI. See the Link Quality Indication section on page 49 for details. x +x +x +1 The CC2420 hardware implementation is shown in Figure 20. Please refer to [1] for further details. In transmit mode the FCS is appended at the correct position defined by the length field. The FCS is not written to the TXFIFO, but stored in a separate 16-bit register. The most significant bit in the last byte of each frame is set high if the CRC of the received frame is correct and low otherwise. In receive mode the FCS is verified by hardware. The user is normally only Data input (LSB first) r0 r1 r2 r3 r4 r5 r6 r7 r8 r9 r10 r11 r12 r13 r14 r15 Figure 20. CC2420 Frame Check Sequence (FCS) hardware implementation [1] SWRS041c Page 38 of 85 CC2420 Length byte Data in RXFIFO n MPDU MPDU1 MPDU2 MPDUn-2 Bit number RSSI (signed) CRC / Corr 7 6 5 4 3 2 1 0 CRC Correlation value (unsigned) OK Figure 21. Data in RXFIFO when MDMCTRL0.AUTOCRC is set 17 RF Data Buffering CC2420 can be configured for different transmit and receive modes, as set in the MDMCTRL1.TX_MODE and MDMCTRL1.RX_MODE control bits. Buffered mode (mode 0) will be used for normal operation of CC2420, while other modes are available for test purposes. 17.1 Buffered transmit mode A TXFIFO underflow is issued if too few bytes are written to the TXFIFO. Transmission is then automatically stopped. The underflow is indicated in the TX_UNDERFLOW status bit, which is returned during each address byte and each byte written to the TXFIFO. The underflow bit is only cleared by issuing a SFLUSHTX command strobe. In buffered transmit mode (TX_MODE 0), the 128 byte TXFIFO, located in CC2420 RAM, is used to buffer data before transmission. A preamble sequence (defined in the Frame Format section below) is automatically inserted before the length field during transmission. The length field must always be the first byte written to the transmit buffer for all frames. The TXFIFO can only contain one data frame at a given time. Writing one or multiple bytes to the TXFIFO is described in the FIFO access section on page 31. Reading data from the TXFIFO is possible with RAM access, but this does not remove the byte from the FIFO. Writing to the TXFIFO after a frame has been transmitted will cause the TXFIFO to be automatically flushed before the new byte is written. The only exception is if a TXFIFO underflow has occurred, then a SFLUSHTX command strobe is required. Transmission is enabled by issuing a STXON or STXONCCA command strobe. See the Radio control state machine section on page 43 for an illustration of how the transmit command strobes affect the state of CC2420. The STXONCCA strobe is ignored if the channel is busy. See the Clear Channel Assessment section on page 50 for details on CCA. The preamble sequence is started 12 symbol periods after the command strobe. After the programmable start of frame delimiter has been transmitted, data is fetched from the TXFIFO. After complete transmission of a data frame, the TXFIFO is automatically refilled with the last transmitted frame. Issuing a new STXON or STXONCCA command strobe will then cause CC2420 to retransmit the last frame. 17.2 Buffered receive mode In buffered receive mode (RX_MODE 0), the 128 byte RXFIFO, located in CC2420 RAM, is used to buffer data received by the demodulator. Accessing data in the RXFIFO is described in the FIFO access section on page 31. The FIFO and FIFOP pins are used to assist the microcontroller in supervising the RXFIFO. Please note that the FIFO and FIFOP pins are only related to the RXFIFO, even if CC2420 is in transmit mode. SWRS041c Page 39 of 85 CC2420 Multiple data frames may be in the RXFIFO simultaneously, as long as the total number of bytes does not exceed 128. See the RXFIFO overflow section on page 33 for details on how a RXFIFO overflow is detected and signalled. 17.3 Unbuffered, serial mode Unbuffered mode should be used for evaluation / debugging purposes only. Buffered mode is recommended for all applications. In unbuffered mode, the FIFO and FIFOP pins are reconfigured as data and data clock pins. The TXFIFO and RXFIFO buffers are not used in this mode. A synchronous data clock is provided by CC2420 at the FIFOP pin, and the FIFO pin is used as data input/output. The FIFOP clock frequency is 250 kHz when active. This is illustrated in Figure 22. Incoming / outgoing RF data Transmit mode: Preamble In serial transmit mode (MDMCTRL1.TX_MODE=1), a synchronisation sequence is inserted at the start of each frame by hardware, as in buffered mode. Data is sampled by CC2420 on the positive edge of FIFOP and should be updated by the microcontroller on the negative edge of FIFOP. See Figure 22 for an illustration of the timing in serial transmit mode. The SFD and CCA pins retain their normal operation also in serial mode. CC2420 will remain in serial transmit mode until transmission is turned off manually. In serial receive mode (MDMCTRL1.RX_MODE=1) byte synchronisation is still performed by CC2420. This means that the FIFOP clock pin will remain inactive until a start of frame delimiter has been detected. SFD s0 s1 s2 4 us FIFOP FIFO (from uC) b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 b11 b8 b9 b10 b11 b0 b1 Receive mode: FIFOP FIFO (from CC2420) b2 b3 b4 Figure 22. Unbuffered test mode, pin activity SWRS041c Page 40 of 85 CC2420 18 Address Recognition CC2420 includes hardware support for address recognition, as specified in [1]. Hardware address recognition may be enabled / disabled using the MDMCTRL0.ADR_DECODE control bit. Address recognition is based on the following requirements, listed from section 7.5.6.2 in [1]: The frame type subfield shall not contain an illegal frame type If the frame type indicates that the frame is a beacon frame, the source PAN identifier shall match macPANId unless macPANId is equal to 0xFFFF, in which case the beacon frame shall be accepted regardless of the source PAN identifier. If a destination PAN identifier is included in the frame, it shall match macPANId or shall be the broadcast PAN identifier (0xFFFF). If a short destination address is included in the frame, it shall match either macShortAddress or the broadcast address (0xFFFF). Otherwise if an extended destination address is included in the frame, it shall match aExtendedAddress. If only source addressing fields are included in a data or MAC command frame, the frame shall only be accepted if the device is a PAN coordinator and the source PAN identifier macPANId. matches If any of the above requirements are not satisfied and address recognition is enabled, CC2420 will disregard the incoming frame and flush the data from the RXFIFO. Only data from the rejected frame is flushed, data from previously accepted frames may still be in the RXFIFO. The IOCFG0.BCN_ACCEPT control bit must be set when the PAN identifier programmed into CC2420 RAM is equal to 0xFFFF and cleared otherwise. This particularly applies to active and passive scans as defined by [1], which requires all received beacons to be processed by the MAC sublayer. Incoming frames with reserved frame types (FCF frame type subfield is 4, 5, 6 or 7) is however accepted if the RESERVED_FRAME_MODE control bit in MDMCTRL0 is set. In this case, no further address recognition is performed on these frames. This option is included for future expansions of the IEEE 802.15.4 standard. If a frame is rejected, CC2420 will only start searching for a new frame after the rejected frame has been completely received (as defined by the length field) to avoid detecting false SFDs within the frame. The MDMCTRL0.PAN_COORDINATOR control bit must be correctly set, since parts of the address recognition procedure requires knowledge about whether the current device is a PAN coordinator or not. 19 Acknowledge Frames CC2420 includes hardware support for transmitting acknowledge frames, as specified in [1]. Figure 23 shows the format of the acknowledge frame. If MDMCTRL0.AUTOACK is enabled, an acknowledge frame is transmitted for all incoming frames accepted by the address recognition with the acknowledge request flag set and a valid CRC. AUTOACK therefore does not make sense unless also ADR_DECODE and AUTOCRC are enabled. The sequence number is copied from the incoming frame. SWRS041c Page 41 of 85 CC2420 AUTOACK may be used for non-beacon systems as long as the frame pending field (see Figure 19) is cleared. The acknowledge frame is then transmitted 12 Bytes: symbol periods after the last symbol of the incoming frame. This is as specified by [1] for non-beacon networks. 1 1 Start of Frame Preamble Frame Delimiter Sequence Length (SFD) Synchronisation Header PHY Header (SHR) (PHR) 1 2 Frame Data Control Field Sequence (FCF) Number MAC Header (MHR) 4 2 Frame Check Sequence (FCS) MAC Footer (MFR) Figure 23. Acknowledge frame format [1] Two command strobes, SACK and SACKPEND are defined to transmit acknowledge frames with the frame pending field cleared or set, respectively. The acknowledge frame is only transmitted if the CRC is valid. For systems using beacons, there is an additional timing requirement that the acknowledge frame transmission should be started on the first backoff-slot boundary (20 symbol periods) at least 12 symbol periods after the last symbol of the incoming frame. This timing must be controlled by the microcontroller by issuing the SACK and SACKPEND command strobe 12 symbol periods before the following backoff-slot boundary, as illustrated in Figure 24. If a SACK or SACKPEND command strobe is issued while receiving an incoming frame, the acknowledge frame is transmitted 12 symbol periods after the last symbol of the incoming frame. This should be used to transmit acknowledge frames in non-beacon networks. This timing is also illustrated in Figure 24. Using SACKPEND will set the pending data flag for automatically transmitted acknowledge frames using AUTOACK. The pending flag will then be set also for future acknowledge frames, until a SACK command strobe is issued. Acknowledge frames may be manually transmitted using normal data transmission if desired. y D ar l nd bo PEN u m K bo sy AC ot U S l D fs / of PP K k t c C s La Ba SA Beacon network PPDU 12 symbol periods 12 symbol periods <= Non-beacon network tack PPDU Acknowledge < 32 symbol periods Acknowledge tack = 12 symbol periods Figure 24. Acknowledge frame timing SWRS041c Page 42 of 85 CC2420 20 Radio control state machine CC2420 has a built-in state machine that is used to switch between different operational states (modes). The change of state is done either by using command strobes or by internal events such as SFD detected in receive mode. The radio control state machine states are shown in Figure 25. The numbers in brackets refer to the state number readable in the FSMSTATE status register. Reading the FSMSTATE status register is primarily for test / debug purposes. Before using the radio in either RX or TX mode, the voltage regulator and crystal oscillator must be turned on and become stable. The voltage regulator and crystal oscillator start-up times are given in the Electrical Specifications section on page 9. The crystal oscillator is controlled by accessing the SXOSCON / SXOSCOFF command strobes. The XOSC16M_STABLE bit in the status register returned during address transfer indicates whether the oscillator is running and stable or not (see Table 5). This status register can be polled when waiting for the oscillator to start. For test purposes, the frequency synthesizer (FS) can also be manually calibrated and started by using the STXCAL command strobe register. This will not start a transmission before a STXON command strobe is issued. This is not shown in Figure 25. Enabling transmission is done by issuing a STXON or STXONCCA command strobe. Turning off RF can be accomplished by using one of the SRFOFF or SXOSCOFF command strobe registers. After reset the CC2420 is in Power Down mode. All configuration registers can then be programmed in order to make the chip ready to operate at the correct frequency and mode. Due to the very fast start-up time, CC2420 can remain in Power Down until a transmission session is requested. As also described in the 4-wire Serial Configuration and Data Interface section on page 27, the crystal oscillator must be running (IDLE) in order to have access to the RAM and FIFOs. SWRS041c Page 43 of 85 CC2420 VREG_EN set low Voltage Regulator Off VREG_EN set high Wait until voltage regulator has powered up Chip Reset (pin or register) SXOSCOFF command strobe All States Crystal oscillator disabled, register access enabled, FIFO / RAM access disabled Power Down (PD) [0] SXOSCON Wait for the specified crystal oscillator start-up time, or poll the XOSC16M_STABLE status bit SRFOFF IDLE [1] N SR XO XO ST RX_CALIBRATE [2 and 40] Preamble and SFD is transmitted Automatic or manual acknowledge request TX_ACK_CALIBRATE [48] ted ple RX_OVERFLOW [17] lo erf m co RX_FRAME [16 and 40] w Ov TX_PREAMBLE [34, 35 and 36] n SFD found SACK or SACKPEND RX_WAIT [14] RX_SFD_SEARCH [3, 4, 5 and 6] Frame received or failed address recognition 8 or 12 symbol periods later io ss HRX SFLUS TX_CALIBRATE [32] i sm an Tr 12 symbol periods later (S ST TX XO ON N CC CCA or A) a nd All RX states N All States except Power Down (PD) TX_FRAME [37, 38 and 39] TXFIFO Data is transmitted Underflow TX_UNDERFLOW [56] The transition from TX_UNDERFLOW to RX_CALIBRATE is automatic, but SFLUSHTX must be used to reset underflow indication 12 symbol periods later TX_ACK_PREAMBLE [49, 50 and 51] Acknowledge completed TX_ACK [52, 53 and 54] Figure 25. Radio control states SWRS041c Page 44 of 85 CC2420 21 MAC Security Operations (Encryption and Authentication) CC2420 features hardware IEEE 802.15.4 MAC security operations. This includes counter mode (CTR) encryption / decryption, CBC-MAC authentication and CCM encryption + authentication. All security operations are based on AES encryption [2] using 128 bit keys. Security operations are performed within the transmit and receive FIFOs on a frame basis. CC2420 also includes stand-alone AES encryption, in which one 128 bit plaintext is encrypted to a 128 bit ciphertext. The SAES, STXENC and SRXDEC command strobes are used to start security operations in CC2420 as will be described in the following sections. The ENC_BUSY status bit (see Table 5) may be used to monitor when a security operation has been completed. Security command strobes issued while the security engine is busy will be ignored, and the ongoing operation will be completed. Table 6 on page 31 shows the CC2420 RAM memory map, including the security related data located from addresses 0x100 through 0x15F. RAM access (see the RAM access section on page 29) is used to write or read the keys, nonces and standalone buffer. All security related data is stored little-endian, i.e. the least significant byte is transferred first over the SPI interface during RAM read or write operations. For a complete description of IEEE 802.15.4 MAC security operations, please refer to [1]. As can be seen from Table 6 on page 31, KEY0 is located from address 0x100 and KEY1 from address 0x130. A way of establishing the keys used for encryption and authentication must be decided for each particular application. IEEE 802.15.4 does not define how this is done, it is left to the higher layer of the protocol. ZigBee uses an Elliptic Curve Cryptography (ECC) based approach to establish keys. For PC based solutions, more processor intensive solutions such as Diffie-Hellman may be chosen. Some applications may also use preprogrammed keys, e.g. for remote keyless entry where the key and lock are delivered in pairs. A push-button approach for loading keys may also be selected. 21.2 Nonce / counter The receive and transmit nonces used for encryption / decryption are located in RAM from addresses 0x110 and 0x140 respectively. They are both 16 bytes. The nonce must be correctly initialized before receive or transmit CTR or CCM operations are started. The format of the nonce is shown in Table 7. The block counter must be set to 1 for compliance with [1]. The key sequence counter is controlled by a layer above the MAC layer. The frame counter must be increased for each new frame by the MAC layer. The source address is the 64 bit IEEE address. 1 byte 8 bytes 4 bytes 1 byte 2 bytes Flags Source Address Frame Counter Key Sequence Counter Block Counter 21.1 Keys All security operations are based on 128 bit keys. The CC2420 RAM space has storage space for two individual keys (KEY0 and KEY1). Transmit, receive and stand-alone encryption may select one of these two keys individually in the SEC_TXKEYSEL, SEC_RXKEYSEL and SEC_SAKEYSEL control bits (SECCTRL0). Table 7. IEEE 802.15.4 Nonce [1] The block counter bytes are not updated in RAM, only in a local copy that is reloaded for each new in-line security operation. I.e. the block counter part of the nonce does not need to be rewritten. The CC2420 block counter should be set to 0x0001 for compliance with [1]. SWRS041c Page 45 of 85 CC2420 CC2420 gives the user full flexibility in selecting the flags for both nonces. The flag setting is stored in the most significant byte of the nonce. The flag byte used for encryption and authentication is then generated as shown in Figure 26. 7 - MSB in CC2420 nonce RAM 6 5 4 3 2 CTR Flag CBC Flag bits 7:6 bits 7:6 7 6 5 Res Res 0 CTR mode flag byte 4 3 2 0 0 1 The frame counter part of the nonce must be incremented for each new packet by software. 0 SECCTRL0.SEC_M L 1 0 7 L Res CBC-MAC flag byte 6 5 4 Adata 3 2 M 1 L Figure 26. CC2420 Security Flag Byte 21.3 Stand-alone encryption Plain AES encryption, with 128 bit plaintext and 128 bit keys [2], is available using stand-alone encryption. The plaintext is stored in stand-alone buffer located at RAM location 0x120, as can be seen from Table 6 on page 31. therefore be operations. used for all security The key, nonce (does not apply to CBCMAC), and SECCTRL0 and SECCTRL1 control registers must be correctly set before starting any in-line security operation. A stand-alone encryption operation is initiated by using the SAES command strobe. The selected key (SECCTRL0.SEC_SAKEYSEL) is then used to encrypt the plaintext written to the stand-alone buffer. Upon completion of the encryption operation, the ciphertext is written back to the stand-alone buffer, thereby overwriting the plaintext. The in-line security mode is set in SECCTRL0.SEC_MODE to one of the following modes: Note that RAM write operations also output data currently in RAM, so that a new plaintext may be written at the same time as reading out the previous ciphertext. When enabled, TX in-line security is started in one of two ways: 21.4 In-line security operations CC2420 can do MAC security operations (encryption, decryption and authentication) on frames within the TXFIFO and RXFIFO. These operations are called in-line security operations. As with other MAC hardware support within CC2420, in-line security operation relies on the length field in the PHY header. A correct length field must Disabled CBC-MAC (authentication) CTR (encryption / decryption) CCM (authentication and encryption / decryption) Issue a STXENC command strobe. Inline security will be performed within the TXFIFO, but a RF transmission will not be started. Ciphertext may be read back using RAM read operations. Issue a STXON or STXONCCA command strobe. In-line security will be performed within the TXFIFO and a RF transmission of the ciphertext is started. When enabled, RX in-line security is started as follows: SWRS041c Page 46 of 85 0 CC2420 Issue a SRXDEC command strobe. The first frame in the RXFIFO is then decrypted / authenticated as set by the current security mode. RX in-line security operations are always performed on the first frame currently inside the RXFIFO, even if parts of this have already been read out over the SPI interface. This allows the receiver to first read the source address out to decide which key to use before doing authentication of the complete frame. In CTR or CCM mode it is of course important that bytes to be decrypted are not read out before the security operation is started. When the SRXDEC command strobe is issued, the FIFO and FIFOP pins will go inactive. This is to indicate to the microcontroller that no further data may be read out before the next byte to be read has undergone the requested security operation. TXFIFO at all, and data will be encrypted as it is written to the TXFIFO. When decryption is initiated with a SRXDEC command strobe, the ciphertext of the RXFIFO is then decrypted as specified by [1]. 21.6 CBC-MAC CBC-MAC in-line authentication provided by CC2420 hardware. is SECCTRL0.SEC_M sets the MIC length M, encoded as (M-2)/2. When enabling CBC-MAC in-line TXFIFO authentication, the generated MIC is written to the TXFIFO for transmission. The frame length must include the MIC. SECCTRL1.SEC_TXL / SEC_RXL sets the number of bytes between the length field and the first byte to be authenticated, normally set to 0 for MAC authentication. The frame in the RXFIFO may be received over RF or it may be written into the RXFIFO over the SPI interface for debugging or higher layer security operations. SECCTRL0.SEC_CBC_HEAD defines if the authentication length is used as the first byte of data to be authenticated or not. This bit should be set for compliance with [1]. 21.5 CTR mode decryption When enabling CBC-MAC in-line RXFIFO authentication, the generated MIC is compared to the MIC in the RXFIFO. The last byte of the MIC is replaced in the RXFIFO with: encryption / CTR mode encryption / decryption is performed by CC2420 on MAC frames within the TXFIFO / RXFIFO respectively. SECCTRL1.SEC_TXL / SEC_RXL sets the number of bytes between the length field and the first byte to be encrypted / decrypted respectively. This controls the number of plaintext bytes in the current frame. For IEEE 802.15.4 MAC encryption, only the MAC payload (see Figure 17 on page 36) should be encrypted, so SEC_TXL / SEC_RXL is set to 3 + (0 to 20) depending on the address information in the current frame. When encryption is initiated, the plaintext in the TXFIFO is then encrypted as specified by [1]. The encryption module will encrypt all the plaintext currently available, and wait if not everything is prebuffered. The encryption operation may also be started without any data in the 0x00 if the MIC is correct 0xFF if the MIC is incorrect The other bytes in the MIC are left unchanged in the RXFIFO. 21.7 CCM CCM combines CTR mode encryption and CBC-MAC authentication in one operation. CCM is described in [3]. SECCTRL1.SEC_TXL / SEC_RXL sets the number of bytes after the length field to be authenticated but not encrypted. The MIC is generated and verified very much like with CBC-MAC described SWRS041c Page 47 of 85 CC2420 above. The only differences are from the requirements in [1] for CCM. 21.8 Timing Table 8 shows some examples of the time used by the security module for different operations. Mode l(a) l(m) l(MIC) Time [us] CCM 50 69 8 222 CTR - 15 - 99 CBC 17 98 12 99 Standalone - 16 - 14 Table 8. Security timing examples 22 Linear IF and AGC Settings CC2420 is based on a linear IF chain where the signal amplification is done in an analog VGA (variable gain amplifier). The gain of the VGA is digitally controlled. The AGC characteristics are set through the AGCCTRL, AGCTST0, AGCTST1 and AGCTST2 registers. The reset values should be used for all AGC control and test registers. The AGC (Automatic Gain Control) loop ensures that the ADC operates inside its dynamic range by using an analog/digital feedback loop. 23 RSSI / Energy Detection CC2420 has a built-in RSSI (Received Signal Strength Indicator) providing a digital value that can be read from the 8 bit, signed 2’s complement RSSI.RSSI_VAL register. where the RSSI_OFFSET is found empirically during system development from the front end gain. RSSI_OFFSET is approximately –45. E.g. if reading a value of –20 from the RSSI register, the RF input power is approximately –65 dBm. The RSSI value is always averaged over 8 symbol periods (128 μs), in accordance with [1]. The RSSI_VALID status bit (Table 5) indicates when the RSSI value is valid, meaning that the receiver has been enabled for at least 8 symbol periods. A typical plot of the RSSI_VAL reading as function of input power is shown in Figure 27. It can be seen from the figure that the RSSI reading from CC2420 is very linear and has a dynamic range of about 100 dB. The RSSI register value RSSI.RSSI_VAL can be referred to the power P at the RF pins by using the following equations: The RSSI register value RSSI.RSSI_VAL is calculated and continuously updated for each symbol after RSSI has become valid. P = RSSI_VAL + RSSI_OFFSET [dBm] SWRS041c Page 48 of 85 CC2420 60 RSSI Register Value 40 20 0 -100 -80 -60 -40 -20 0 -20 -40 -60 RF Level [dBm] Figure 27. Typical RSSI value vs. input power 24 Link Quality Indication The link quality indication (LQI) measurement is a characterisation of the strength and/or quality of a received packet, as defined by [1]. The RSSI value described in the previous section may be used by the MAC software to produce the LQI value. The LQI value is required by [1] to be limited to the range 0 through 255, with at least 8 unique values. Software is responsible for generating the appropriate scaling of the LQI value for the given application. Using the RSSI value directly to calculate the LQI value has the disadvantage that e.g. a narrowband interferer inside the channel bandwidth will increase the LQI value although it actually reduces the true link quality. CC2420 therefore also provides an average correlation value for each incoming packet, based on the 8 first symbols following the SFD. This unsigned 7-bit value can be looked upon as a measurement of the “chip error rate,” although CC2420 does not do chip decision. As described in the Frame check sequence section on page 38, the average correlation value for the 8 first symbols is appended to each received frame together with the RSSI and CRC OK/not OK when MDMCTRL0.AUTOCRC is set. A correlation value of ~110 indicates a maximum quality frame while a value of ~50 is typically the lowest quality frames detectable by CC2420. Software must convert the correlation value to the range 0-255 defined by [1], e.g. by calculating: LQI = (CORR – a) · b limited to the range 0-255, where a and b are found empirically based on PER measurements as a function of the correlation value. A combination of RSSI and correlation values may also be used to generate the LQI value. SWRS041c Page 49 of 85 CC2420 25 Clear Channel Assessment The clear channel assessment signal is based on the measured RSSI value and a programmable threshold. The clear channel assessment function is used to implement the CSMA-CA functionality specified in [1]. CCA is valid when the receiver has been enabled for at least 8 symbol periods. Carrier sense threshold level is programmed by RSSI.CCA_THR. The threshold value can be programmed in steps of 1 dB. A CCA hysteresis can also be programmed in the MDMCTRL0.CCA_HYST control bits. All 3 CCA modes specified by [1] are implemented in CC2420. They are set in MDMCTRL0.CCA_MODE, as can be seen in the register description. The different modes are: 0 Reserved 1 Clear channel when received energy is below threshold. 2 Clear channel when not receiving valid IEEE 802.15.4 data. 3 Clear channel when energy is below threshold and not receiving valid IEEE 802.15.4 data Clear channel assessment is available on the CCA output pin. CCA is active high, but the polarity may be changed by setting the IOCFG0.CCA_POLARITY control bit. Implementing CSMA-CA may easiest be done by using the STXONCCA command strobe, as described in the Radio control state machine section on page 43. Transmission will then only start if the channel is clear. The TX_ACTIVE status bit (see Table 5) may be used to detect the result of the CCA. 26 Frequency and Channel Programming The operating frequency is set by programming the 10 bit frequency word located in FSCTRL.FREQ[9:0]. The operating frequency FC in MHz is given by: IEEE 802.15.4 specifies 16 channels within the 2.4 GHz band, in 5 MHz steps, numbered 11 through 26. The RF frequency of channel k is given by [1]: FC = 2048 + FSCTRL.FREQ[9:0] MHz FC = 2405 + 5 (k-11) MHz, k=11, 12, ..., 26 The frequency can be programmed with 1 MHz resolution. In receive mode the actual LO frequency is FC – 2 MHz, since a 2 MHz IF is used. Direct conversion is used for transmission, so here the LO frequency equals FC. The 2 MHz IF is automatically set by CC2420, so the frequency programming is equal for RX and TX. For operation in channel k, the FSCTRL.FREQ register should therefore be set to: FSCTRL.FREQ = 357 + 5 (k-11) SWRS041c Page 50 of 85 CC2420 27 VCO and PLL Self-Calibration In order to ensure reliable operation the VCO’s bias current and tuning range are automatically calibrated every time the RX mode or TX mode is enabled, i.e. in the RX_CALIBRATE, TX_CALIBRATE and TX_ACK_CALIBRATE control states in Figure 25 on page 44. 27.1 VCO The VCO is completely integrated and operates at 4800 – 4966 MHz. The VCO frequency is divided by 2 to generate frequencies in the desired band (24002483.5 MHz). 27.2 PLL self-calibration The VCO's characteristics will vary with temperature, changes in supply voltages, and the desired operating frequency. 28 Output Power Programming The RF output power of the device is programmable and is controlled by the TXCTRL.PA_LEVEL register. Table 9 shows the output power for different settings, including the complete programming of the TXCTRL control register. The typical current consumption is also shown. PA_LEVEL TXCTRL register Output Power [dBm] Current Consumption [mA] 31 0xA0FF 0 17.4 27 0xA0FB -1 16.5 23 0xA0F7 -3 15.2 19 0xA0F3 -5 13.9 15 0xA0EF -7 12.5 11 0xA0EB -10 11.2 7 0xA0E7 -15 9.9 3 0xA0E3 -25 8.5 Table 9. Output power settings and typical current consumption @ 2.45 GHz 29 Voltage Regulator CC2420 includes a low drop-out voltage regulator. This is used to provide a 1.8 V power supply to the CC2420 power supplies. The voltage regulator should not be used to provide power to other circuits because of limited power sourcing capability and noise considerations. The voltage regulator input pin VREG_IN is connected to the unregulated 2.1 to 3.6 V power supply. The voltage regulator is enabled / disabled using the active high voltage regulator enable pin VREG_EN. The regulated 1.8 V voltage output is available on the VREG_OUT pin. A simplified schematic of the voltage regulator is shown in Figure 28. The voltage regulator requires external components as described in the Application Circuit section on page 19. When disabling the voltage regulator, note that register and RAM programming will be lost as leakage current reduces the output voltage on the VREG_OUT pin below 1.6 V. SWRS041c Page 51 of 85 CC2420 CC2420 should then be reset before the be left open. Note that the battery monitor will not work when the voltage regulator is not used. voltage regulator is disabled. In applications where the internal voltage regulator is not used, connect VREG_EN and VREG_IN to ground. VREG_OUT shall VREG_EN VREG_IN Regulator Enable / disable Internal bandgap voltage reference 1.25 V VREG_OUT Figure 28. Voltage regulator, simplified schematic 30 Battery Monitor The on-chip battery monitor enables monitoring the unregulated voltage on the VREG_IN pin. It gives status information on the voltage being above or below a programmable threshold. A simplified schematic of the battery monitor is shown in Figure 29. SWRS041c Page 52 of 85 CC2420 BATTMON.BATTMON_EN Internal bandgap voltage reference VREG_IN 1.25 V BATTMON.BATTMON_OK BATTMON.BATTMON_VOLTAGE[4:0] Figure 29. Battery monitor, simplified schematic The battery monitor is controlled through the BATTMON control register. The battery monitor is enabled and disabled using the BATTMON.BATTMON_EN control bit. The voltage regulator must also be enabled when using the battery monitor. The battery monitor status bit is available in the BATTMON.BATTMON_OK status bit. This bit is high when the VREG_IN input voltage is higher than the toggle voltage Vtoggle. The battery monitor toggle voltage is set in the 5-bit BATTMON.BATTMON_VOLTAGE control bits. BATTMON_VOLTAGE is an unsigned, positive number from 0 to 31. The toggle voltage is given by: V toggle 1.25 V 72 BATTMON_VO LTAGE 27 Alternatively, for a desired toggle voltage, BATTMON_VOLTAGE should be set according to: BATTMON_VO LTAGE 72 27 V toggle 1.25 V The voltage regulator must be enabled for at least 100 μs before the first measurement. After being enabled, the BATTMON_OK status bit needs 2 μs to settle for each new toggle voltage programmed. The main performance characteristics of the battery monitor is shown in the Electrical Specifications section on page 9. 31 Crystal Oscillator An external clock signal or the internal crystal oscillator can be used as main frequency reference. The reference frequency must be 16 MHz. Because the crystal frequency is used as reference for the data rate as well as other internal signal processing functions, other frequencies cannot be used. If an external clock signal is used this should be connected to XOSC16_Q1, while XOSC16_Q2 should be left open. The MAIN.XOSC16M_BYPASS bit must be set when an external clock signal is used. Using the internal crystal oscillator, the crystal must be connected between the XOSC16_Q1 and XOSC16_Q2 pins. The oscillator is designed for parallel mode operation of the crystal. In addition, loading capacitors (C381 and C391) for the crystal are required. The loading capacitor values depend on the total load capacitance, CL, specified for the crystal. SWRS041c Page 53 of 85 CC2420 The total load capacitance seen between the crystal terminals should equal CL for the crystal to oscillate at the specified frequency. CL 1 1 1 C381 C391 The crystal oscillator circuit is shown in Figure 30. Typical component values for different values of CL are given in Table 10. The crystal oscillator is amplitude regulated. This means that a high current is used to start up the oscillations. When the amplitude builds up, the current is reduced to what is necessary to maintain a stable oscillation. This ensures a fast startup and keeps the drive level to a minimum. The ESR of the crystal must be within the specification in order to ensure a reliable start-up (see the Electrical Specifications section). C parasitic The parasitic capacitance is constituted by pin input capacitance and PCB stray capacitance. The total parasitic capacitance is typically 2 pF - 5 pF. XOSC16_Q1 XOSC16_Q2 XTAL C391 C381 Figure 30. Crystal oscillator circuit Item CL= 16 pF C381 27 pF C391 27 pF Table 10. Crystal oscillator component values 32 Input / Output Matching The RF input / output is differential (RF_N and RF_P). In addition there is supply switch output pin (TXRX_SWITCH) that must have an external DC path to RF_N and RF_P. In RX mode the TXRX_SWITCH pin is at ground and will bias the LNA. In TX mode the TXRX_SWITCH pin is at supply rail voltage and will properly bias the internal PA. The RF output and DC bias can be done using different topologies. Some are shown in Figure 4 and Figure 5. Component values are given in Table 2. Using a differential antenna, no balun is required. If a single ended output is required (for a single ended connector or a single ended antenna), a balun should be used for optimum performance. The balun adds the signals from the RF_N and RF_P. This is achieved having two paths with equal amplitude response, but 180 degrees phase difference. SWRS041c Page 54 of 85 CC2420 33 Transmitter Test Modes CC2420 can be set into different transmit test modes for performance evaluation. The test mode descriptions in the following sections requires that the chip is first reset, the crystal oscillator is enabled using the SXOSCON command strobe and that the crystal oscillator has stabilised. 0x1800 to the DACTST register and issue a STXON command strobe. The transmitter is then enabled while the transmitter I/Q DACs are overridden to static values. An unmodulated carrier will then be available on the RF output pins. A plot of the single carrier output spectrum from CC2420 is shown in Figure 31 below. 33.1 Unmodulated carrier An unmodulated carrier may be transmitted by setting MDMCTRL1.TX_MODE to 2 or 3, writing RBW 10 kHz Ref Lvl VBW 10 kHz 3 dBm SWT 50 ms RF Att Unit 30 dB dBm 3 0 A -10 -20 -30 1AVG 1SA -40 -50 -60 -70 -80 -90 -97 Center 2.45 GHz Date: 23.OCT.2003 200 kHz/ Span 2 MHz 21:38:33 Figure 31. Single carrier output SWRS041c Page 55 of 85 CC2420 sequence for bit error testing. Please note that CC2420 requires symbol synchronisation, not only bit synchronisation, for correct reception. Packet error rate is therefore a better measurement for the true RF performance. 33.2 Modulated spectrum The CC2420 has a built-in test pattern generator that can generate pseudo random sequence using the CRC generator. This is enabled by setting MDMCTRL1.TX_MODE to 3 and issues an STXON command strobe. The modulated spectrum is then available on the RF pins. The low byte of the CRC word is transmitted and the CRC is updated with 0xFF for each new byte. The length of the transmitted data sequence is 65535 bits. The transmitted data-sequence is then: [Synchronisation header] [0x00, 0xb8, 0x4b, 0x99, 0xc3, 0xe9, …] Another option to generate a modulated spectrum is to fill the TXFIFO with pseudorandom data and set MDMCTRL1.TX_MODE to 2. CC2420 will then transmit data from the FIFO disregarding a TXFIFO underflow. The length of the transmitted data sequence is then 1024 bits (128 bytes). 0x78, A plot of the modulated spectrum from CC2420 is shown in Figure 32. Note that to find the output power from the modulated spectrum, the RBW must be set to 3 MHz or higher. Since a synchronisation header (preamble and SFD) is transmitted in all TX modes, this test mode may also be used to transmit a known pseudorandom bit RBW 100 kHz Ref Lvl VBW 100 kHz 0 dBm SWT 5 ms RF Att Unit 30 dB dBm 0 A -10 -20 -30 1AVG 1SA -40 -50 -60 -70 -80 -90 -100 Center 2.45 GHz Date: 23.OCT.2003 1 MHz/ Span 10 MHz 21:34:19 Figure 32. Modulated spectrum plot SWRS041c Page 56 of 85 CC2420 34 System Considerations and Guidelines SRD regulations International regulations and national laws regulate the use of radio receivers and transmitters. SRDs (Short Range Devices) for license free operation are allowed to operate in the 2.4 GHz band worldwide. The most important regulations are ETSI EN 300 328 and EN 300 440 (Europe), FCC CFR-47 part 15.247 and 15.249 (USA), and ARIB STD-T66 (Japan). 34.1 Frequency hopping and multichannel systems The 2.4 GHz band is shared by many systems both in industrial, office and home environments. CC2420 uses direct sequence spread spectrum (DSSS) as defined by [1] to spread the output power, thereby making the communication link more robust even in a noisy environment. With CC2420 it is also possible to combine both DSSS and FHSS (frequency hopping spread spectrum) in a proprietary nonIEEE 802.15.4 system. This is achieved by reprogramming the operating frequency (see the Frequency and Channel Programming section on page 50) before enabling RX or TX. A frequency synchronisation scheme must then be implemented within the proprietary MAC layer to make the transmitter and receiver operate on the same RF channel. 34.2 Data burst transmissions The data buffering in CC2420 lets the user have a lower data rate link between the microcontroller and the RF device than the RF bit rate of 250 kbps. This allows the microcontroller to buffer data at its own speed, reducing the workload and timing requirements. The relatively high data rate of CC2420 also reduces the average power consumption compared to the 868 / 915 MHz bands defined by [1], where only 20 / 40 kbps are available. CC2420 may be powered up a smaller portion of the time, so that the average power consumption is reduced for a given amount of data to be transferred. 34.3 Crystal accuracy and drift A crystal accuracy of ±40 ppm is required for compliance with IEEE 802.15.4 [1]. This accuracy must also take ageing and temperature drift into consideration. A crystal with low temperature drift and low aging could be used without further compensation. A trimmer capacitor in the crystal oscillator circuit (in parallel with C7) could be used to set the initial frequency accurately. For non-IEEE 802.15.4 systems, the robust demodulator in CC2420 allows up to 120 ppm total frequency offset between the transmitter and receiver. This could e.g. relax the accuracy requirement to 60 ppm for each of the devices. Optionally in a star network topology, the FFD could be equipped with a more accurate crystal thereby relaxing the requirement on the RFD. This can make sense in systems where the RFDs ship in higher volumes than the FFDs. 34.4 Communication robustness CC2420 provides very good adjacent, alternate and co channel rejection, image frequency suppression and blocking properties. The CC2420 performance is significantly better than the requirements imposed by [1]. These are highly important parameters for reliable operation in the 2.4 GHz band, since an increasing number of devices/systems are using this license free frequency band. 34.5 Communication security The hardware encryption and authentication operations in CC2420 enable secure communication, which is required for many applications. Security operations require a lot of data processing, which is costly in an 8-bit microcontroller system. The hardware support within CC2420 enables a high level of security even with a low-cost 8 bit controller. SWRS041c Page 57 of 85 CC2420 required to synchronisation. 34.6 Low-cost systems As the CC2420 provides 250 kbps multichannel performance without any external filters, a very low-cost system can be made. A differential antenna will eliminate the need for a balun, and the DC biasing can be achieved in the antenna topology. re-gain In an IEEE 802.15.4 system, all communication is based on packets. The sensitivity limit specified by [1] is based on Packet Error Rate (PER) measurements instead of BER. This is a more accurate measurement of the true RF performance since it mirrors the way the actual system operates. 34.7 Battery operated systems In low power applications, the CC2420 should be powered down when not being active. Extremely low power consumption may be achieved when disabling also the voltage regulator. This will require reprogramming of the register and RAM configuration. It is recommended to perform PER measurements instead of BER measurements to evaluate the performance of IEEE 802.15.4 systems. To do PER measurements, the following may be used as a guideline: A valid preamble, SFD and length field must be used for each packet. The PSDU (see Figure 17 on page 36) length should be 20 bytes for sensitivity measurements as specified by [1]. The sensitivity limit specified by [1] is the RF level resulting in a 1% PER. The packet sample space for a given measurement must then be >> 100 to have a sufficiently large sample space. E.g. at least 1000 packets should be used to measure the sensitivity. The data transmitted over air must be spread according to [1] and the description on page 24. Pregenerated packets may be used, although [1] requires that the PER is averaged over random PSDU data. The CC2420 receive FIFO may be used to buffer data received during PER measurements, since it is able to buffer up to 128 bytes. The MDMCTRL1.CORR_THR control register is by default set to 20, as described in the Demodulator, Symbol Synchroniser and Data Decision section. 34.8 BER / PER measurements CC2420 includes test modes where data is received infinitely and output to pins (RX_MODE 2, see page 40). This mode may be used for Bit Error Rate (BER) measurements. However, the following actions must be taken to do such a measurement: A preamble and SFD sequence must be used, even if pseudo random data is transmitted, since receiving the DSSS modulated signal requires symbol synchronisation, not bit synchronisation like e.g. in 2FSK systems. The SYNCWORD may be set to another value to fit to the measurement setup if necessary. The data transmitted over air must be spread according to [1] and the description on page 24. This means that the transmitter used during measurements must be able to do spreading of the bit data to chip data. Remember that the chip sequence transmitted by the test setup is not the same as the bit sequence, which is output by CC2420. When operating at or below the sensitivity limit, CC2420 may loose symbol synchronisation in infinite receive mode. A new SFD and restart of the receiver may be SWRS041c Page 58 of 85 CC2420 The RXCTRL1.RXBPF_LOCUR control bit should be set to 1. signal has the same phase shifts as the OQPSK sequence previously defined. The simplest way of making a PER measurement will be to use another CC2420 as the reference transmitter. However, this makes it difficult to measure the exact receiver performance. For a desired symbol sequence s0, s1, … , sn-1 of length n symbols, the desired chip sequence c0, c1, c2, …, c32n-1 of length 32n is found using table lookup from Table 3 on page 24. It can be seen from comparing the phase shifts of the O-QPSK signal with the frequency of a MSK signal that the MSK chip sequence is generated as: Using a signal generator, this may either be set up as O-QPSK with half-sine shaping or as MSK. If using O-QPSK, the phases must be selected according to [1]. If using MSK, the chip sequence must be modified such that the modulated MSK (c0 xnor c1), (c1 xor c2), (c2 xnor c3), … , (c32n-1 xor c32n) where c32n may be arbitrarily selected. 35 PCB Layout Recommendations Following Texas Instruments’s reference design is highly recommended. vias. Supply important. power filtering is very In our reference design, the top layer is used for signal routing, and the open areas are filled with metallisation connected to ground using several vias. Layer 2 has not been used in our CC2420 reference designs. Layer 3 is used for power routing and the bottom layer serves as ground plane with a little routing. The external components should be as small as possible (0402 is recommended) and surface mount devices must be used. Caution should be used when placing the microcontroller in order to avoid interference with the RF circuitry. The area under the chip is used for grounding and must be well connected to the ground plane with several vias. A Development Kit with a fully assembled Evaluation Module is available. It is strongly advised that this reference layout is followed very closely in order to get the best performance. The ground pins should be connected to ground as close as possible to the package pin using individual vias. The decoupling capacitors should also be placed as close as possible to the supply pins and connected to the ground plane by separate The schematic, BOM and layout Gerber files for the reference designs are all available from the Texas Instruments website. 36 Antenna Considerations CC2420 can be used together with various types of antennas. A differential antenna like a dipole would be the easiest to interface not needing a balun (balanced to un-balanced transformation network). The length of the /2-dipole antenna is given by: L = 14250 / f where f is in MHz, giving the length in cm. An antenna for 2450 MHz should be 5.8 cm. Each arm is therefore 2.9 cm. Other commonly used antennas for shortrange communication are monopole, helical and loop antennas. The singleended monopole and helical would require a balun network between the differential output and the antenna. Monopole antennas are resonant antennas with a length corresponding to one quarter of the electrical wavelength (/4). They are very easy to design and can be implemented simply as a “piece of wire” or even integrated into the PCB. SWRS041c Page 59 of 85 CC2420 The length of the /4-monopole antenna is given by: L = 7125 / f Helical antennas can be thought of as a combination of a monopole and a loop antenna. They are a good compromise in size critical applications. Helical antennas tend to be more difficult to optimize than the simple monopole. where f is in MHz, giving the length in cm. An antenna for 2450 MHz should be 2.9 cm. Loop antennas are easy to integrate into the PCB, but are less effective due to difficult impedance matching because of their very low radiation resistance. Non-resonant monopole antennas shorter than /4 can also be used, but at the expense of range. In size and cost critical applications such an antenna may very well be integrated into the PCB. For low power applications the differential antenna is recommended giving the best range and because of its simplicity. Enclosing the antenna in high dielectric constant material reduces the overall size of the antenna. Many vendors offer such antennas intended for PCB mounting. The antenna should be connected as close as possible to the IC. If the antenna is located away from the RF pins the antenna should be matched to the feeding transmission line (50 ). SWRS041c Page 60 of 85 CC2420 37 Configuration Registers The configuration of CC2420 is done by programming the 16-bit configuration registers. Complete descriptions of the registers are given in the following tables. After chip reset (from the RESETn pin or programmable through the MAIN.RESETn configuration bit), all the registers have default values as shown in the tables. in Table 11. Many of these registers are for test purposes only, and need not be accessed for normal operation of CC2420. The FIFOs are accessed through two 8-bit registers, TXFIFO and RXFIFO. The TXFIFO register is write only. Data may still be read out of the TXFIFO through regular RAM access (see section RAM access section on page 29), but data is then not removed from the FIFO. Note that the crystal oscillator must be active for all FIFO and RAM access. Note that the MAIN register is only reset by using the pin reset RESETn. When writing to this register, all bits will get the value written, not the default value. This also means that the MAIN.RESETn bit must be written both low and then high to perform a chip reset through the serial interface. During address transfer, and while data is being written to the TXFIFO, a status byte is returned on the serial data output pin SO. This status byte is described in Table 5 on page 29. 15 registers are Strobe Command Registers, listed first in Table 11 below. Accessing these registers will initiate the change of an internal state or mode. There are 33 normal 16-bits registers, also listed All configuration and status registers are described in the tables following Table 11. Address Register Register type Description 0x00 SNOP S No Operation (has no other effect than reading out status-bits) 0x01 SXOSCON S Turn on the crystal oscillator (set XOSC16M_PD = 0 and BIAS_PD = 0) 0x02 STXCAL S Enable and calibrate frequency synthesizer for TX; Go from RX / TX to a wait state where only the synthesizer is running. 0x03 SRXON S Enable RX 0x04 STXON S Enable TX after calibration (if not already performed) Start TX in-line encryption if SPI_SEC_MODE 0 0x05 STXONCCA S If CCA indicates a clear channel: Enable calibration, then TX. Start in-line encryption if SPI_SEC_MODE 0 else do nothing 0x06 SRFOFF S Disable RX/TX and frequency synthesizer 0x07 SXOSCOFF S Turn off the crystal oscillator and RF 0x08 SFLUSHRX S Flush the RX FIFO buffer and reset the demodulator. Always read at least one byte from the RXFIFO before issuing the SFLUSHRX command strobe 0x09 SFLUSHTX S Flush the TX FIFO buffer 0x0A SACK S Send acknowledge frame, with pending field cleared. 0x0B SACKPEND S Send acknowledge frame, with pending field set. 0x0C SRXDEC S Start RXFIFO in-line decryption / authentication (as set by SPI_SEC_MODE) 0x0D STXENC S Start TXFIFO in-line encryption / authentication (as set by SPI_SEC_MODE), without starting TX. SWRS041c Page 61 of 85 CC2420 Address Register Register type Description 0x0E SAES S AES Stand alone encryption strobe. SPI_SEC_MODE is not required to be 0, but the encryption module must be idle. If not, the strobe is ignored. 0x0F - - Not used 0x10 MAIN R/W Main Control Register 0x11 MDMCTRL0 R/W Modem Control Register 0 0x12 MDMCTRL1 R/W Modem Control Register 1 0x13 RSSI R/W RSSI and CCA Status and Control register 0x14 SYNCWORD R/W Synchronisation word control register 0x15 TXCTRL R/W Transmit Control Register 0x16 RXCTRL0 R/W Receive Control Register 0 0x17 RXCTRL1 R/W Receive Control Register 1 0x18 FSCTRL R/W Frequency Synthesizer Control and Status Register 0x19 SECCTRL0 R/W Security Control Register 0 0x1A SECCTRL1 R/W Security Control Register 1 0x1B BATTMON R/W Battery Monitor Control and Status Register 0x1C IOCFG0 R/W Input / Output Control Register 0 0x1D IOCFG1 R/W Input / Output Control Register 1 0x1E MANFIDL R/W Manufacturer ID, Low 16 bits 0x1F MANFIDH R/W Manufacturer ID, High 16 bits 0x20 FSMTC R/W Finite State Machine Time Constants 0x21 MANAND R/W Manual signal AND override register 0x22 MANOR R/W Manual signal OR override register 0x23 AGCCTRL R/W AGC Control Register 0x24 AGCTST0 R/W AGC Test Register 0 0x25 AGCTST1 R/W AGC Test Register 1 0x26 AGCTST2 R/W AGC Test Register 2 0x27 FSTST0 R/W Frequency Synthesizer Test Register 0 0x28 FSTST1 R/W Frequency Synthesizer Test Register 1 0x29 FSTST2 R/W Frequency Synthesizer Test Register 2 0x2A FSTST3 R/W Frequency Synthesizer Test Register 3 0x2B RXBPFTST R/W Receiver Bandpass Filter Test Register 0x2C FSMSTATE R Finite State Machine State Status Register 0x2D ADCTST R/W ADC Test Register 0x2E DACTST R/W DAC Test Register 0x2F TOPTST R/W Top Level Test Register 0x30 RESERVED R/W Reserved for future use control / status register 0x310x3D - - 0x3E TXFIFO W Transmit FIFO Byte Register 0x3F RXFIFO R/W Receiver FIFO Byte Register Not used R/W - Read/write (control/status), R - Read only, W – Write only, S – Command Strobe (perform action upon access) Table 11. Configuration registers overview SWRS041c Page 62 of 85 CC2420 MAIN (0x10) - Main Control Register Bit Field Name Reset R/W Description 15 RESETn 1 R/W Active low reset of the entire circuit should be applied before doing anything else. Equivalent to using the RESETn reset pin. 14 ENC_RESETn 1 R/W Active low reset of the encryption module. (Test purposes only) 13 DEMOD_RESETn 1 R/W Active low reset of the demodulator module. (Test purposes only) 12 MOD_RESETn 1 R/W Active low reset of the modulator module. (Test purposes only) 11 FS_RESETn 1 R/W Active low reset of the frequency synthesizer module. (Test purposes only) 10:1 - 0 W0 Reserved, write as 0 0 XOSC16M_BYPASS 0 R/W Bypasses the crystal oscillator and uses a buffered version of the signal on Q1 directly. This can be used to apply an external rail-rail clock signal to the Q1 pin. SWRS041c Page 63 of 85 CC2420 MDMCTRL0 (0x11) - Modem Control Register 0 Bit Field Name Reset R/W Description 15:14 - 0 W0 Reserved, write as 0 13 RESERVED_FRAME_MODE 0 R/W Mode for accepting reserved IEE 802.15.4 frame types when address recognition is enabled (MDMCTRL0.ADR_DECODE = 1). 0 : Reserved frame types (100, 101, 110, 111) are rejected by address recognition. 1 : Reserved frame types (100, 101, 110, 111) are always accepted by address recognition. No further address decoding is done. When address recognition is disabled (MDMCTRL0.ADR_DECODE = 0), all frames are received and RESERVED_FRAME_MODE is don’t care. 12 PAN_COORDINATOR 0 R/W Should be set high when the device is a PAN Coordinator. Used for filtering packets with no destination address, as specified in section 7.5.6.2 in 802.15.4, D18 11 ADR_DECODE 1 R/W Hardware Address decode enable. 0 : Address decoding is disabled 1 : Address decoding is enabled 10:8 CCA_HYST[2:0] 2 R/W CCA Hysteresis in dB, values 0 through 7 dB 7:6 CCA_MODE[1:0] 3 R/W 0 : Reserved 1 : CCA=1 when RSSI_VAL < CCA_THR - CCA_HYST CCA=0 when RSSI_VAL ≥ CCA_THR 2 : CCA=1 when not receiving valid IEEE 802.15.4 data, CCA=0 otherwise 3 : CCA=1 when RSSI_VAL < CCA_THR - CCA_HYST and not receiving valid IEEE 802.15.4 data. CCA=0 when RSSI_VAL ≥ CCA_THR or receiving a packet 5 AUTOCRC 1 R/W In packet mode a CRC-16 (ITU-T) is calculated and is transmitted after the last data byte in TX. In RX CRC is calculated and checked for validity. 4 AUTOACK 0 R/W If AUTOACK is set, all packets accepted by address recognition with the acknowledge request flag set and a valid CRC are acknowledged 12 symbol periods after being received. 3:0 PREAMBLE_LENGTH [3:0] 2 R/W The number of preamble bytes (2 zero-symbols) to be sent in TX mode prior to the SYNCWORD, encoded in steps of 2. The reset value of 2 is compliant with IEEE 802.15.4, since the 4th zero byte is included in the SYNCWORD. 0 : 1 leading zero bytes (not recommended) 1 : 2 leading zero bytes (not recommended) 2 : 3 leading zero bytes (IEEE 802.15.4 compliant) 3 : 4 leading zero bytes … 15 : 16 leading zero bytes SWRS041c Page 64 of 85 CC2420 MDMCTRL1 (0x12)– Modem Control Register 1 Bit Field Name Reset R/W Description 15:11 - 0 W0 Reserved, write as 0. 10:6 CORR_THR[4:0] 20 R/W Demodulator correlator threshold value, required before SFD search. Note that on early CC2420 versions the reset value was 0. 5 DEMOD_AVG_MODE 0 R/W Frequency offset average filter behaviour. 0 : Lock frequency offset filter after preamble match 1 : Continuously update frequency offset filter. 4 MODULATION_MODE 0 R/W Set one of two RF modulation modes for RX / TX 0 : IEEE 802.15.4 compliant mode 1 : Reversed phase, non-IEEE compliant (could be used to set up a system which will not receive 802.15.4 packets) 3:2 TX_MODE[1:0] 0 R/W Set test modes for TX 0 : Buffered mode, use TXFIFO (normal operation) 1 : Serial mode, use transmit data on serial interface, infinite transmission. For lab testing only. 2 : TXFIFO looping ignore underflow in TXFIFO and read cyclic, infinite transmission. For lab testing only. 3 : Send random data from CRC, infinite transmission. For lab testing only. 1:0 RX_MODE[1:0] 0 R/W Set test mode of RX 0 : Buffered mode, use RXFIFO (normal operation) 1 : Receive serial mode, output received data on pins. Infinite RX. For lab testing only. 2 : RXFIFO looping ignore overflow in RXFIFO and write cyclic, infinite reception. For lab testing only. 3 : Reserved RSSI (0x13) - RSSI and CCA Status and Control Register Bit 15:8 Field Name Reset R/W Description CCA_THR[7:0] -32 R/W Clear Channel Assessment threshold value, signed number on 2’s complement for comparison with the RSSI. The unit is 1 dB, offset is the same as for RSSI_VAL. The CCA signal goes active when the received signal is below this value. The CCA signal is available on the CCA pin. The reset value is approximately -77 dBm. 7:0 RSSI_VAL[7:0] -128 R RSSI estimate on a logarithmic scale, signed number on 2’s complement. Unit is 1 dB, offset is described in the RSSI / Energy Detection section on page 48. The RSSI_VAL value is averaged over 8 symbol periods. The RSSI_VALID status bit may be checked to verify that the receiver has been enabled for at least 8 symbol periods. The reset value of –128 also indicates that the RSSI_VAL value is invalid. SWRS041c Page 65 of 85 CC2420 SYNCWORD (0x14) - Sync Word Bit 15:0 Field Name Reset R/W Description SYNCWORD[15:0] 0xA70F R/W Synchronisation word. The SYNCWORD is processed from the least significant nibble (F at reset) to the most significant nibble (A at reset). SYNCWORD is used both during modulation (where 0xF’s are replaced with 0x0’s) and during demodulation (where 0xF’s are not required for frame synchronisation). In reception an implicit zero is required before the first symbol required by SYNCWORD. The reset value is compliant with IEEE 802.15.4. TXCTRL (0x15) - Transmit Control Register Bit 15:14 Field Name Reset R/W Description TXMIXBUF_CUR[1:0] 2 R/W TX mixer buffer bias current. 0: 690uA 1: 980uA 2: 1.16mA (nominal) 3: 1.44mA 13 TX_TURNAROUND 1 R/W Sets the wait time after STXON before transmission is started. 0 : 8 symbol periods (128 us) 1 : 12 symbol periods (192 us) 12:11 TXMIX_CAP_ARRAY[1:0] 0 R/W Selects varactor array settings in the transmit mixers. 10:9 TXMIX_CURRENT[1:0] 0 R/W Transmit mixers current: 0: 1.72 mA 1: 1.88 mA 2: 2.05 mA 3: 2.21 mA 8:6 PA_CURRENT[2:0] 3 R/W Current programming of the PA 0: -3 current adjustment 1: -2 current adjustment 2: -1 current adjustment 3: Nominal setting 4: +1 current adjustment 5: +2 current adjustment 6: +3 current adjustment 7: +4 current adjustment 5 - 1 W1 Reserved, write as 1. 4:0 PA_LEVEL[4:0] 31 R/W Output PA level. (~0 dBm) SWRS041c Page 66 of 85 CC2420 RXCTRL0 (0x16) – Receive control register 0 Bit Field Name Reset R/W Description 15:14 - 0 W0 Reserved, write as 0. 13:12 RXMIXBUF_CUR[1:0] 1 R/W RX mixer buffer bias current. 0: 690uA 1: 980uA (nominal) 2: 1.16mA 3: 1.44mA 11:10 HIGH_LNA_GAIN[1:0] 0 R/W Controls current in the LNA gain compensation branch in AGC High gain mode. 0: Compensation disabled 1: 100 µA compensation current 2: 300 µA compensation current (Nominal) 3: 1000 µA compensation current 9:8 MED_LNA_GAIN[1:0] 2 R/W Controls current in the LNA gain compensation branch in AGC Med gain mode. 7:6 LOW_LNA_GAIN[1:0] 3 R/W Controls current in the LNA gain compensation branch in AGC Low gain mode 5:4 HIGH_LNA_CURRENT[1:0] 2 R/W Controls main current in the LNA in AGC High gain mode 0: 240 µA LNA current (x2) 1: 480 µA LNA current (x2) 2: 640 µA LNA current (x2) 3: 1280 µA LNA current (x2) 3:2 MED_LNA_CURRENT[1:0] 1 R/W Controls main current in the LNA in AGC Med gain mode 1:0 LOW_LNA_CURRENT[1:0] 1 R/W Controls main current in the LNA in AGC Low gain mode SWRS041c Page 67 of 85 CC2420 RXCTRL1 (0x17) - Receive control register 1 Bit Field Name Reset R/W Description 15:14 - 0 W0 Reserved, write as 0. 13 RXBPF_LOCUR 0 R/W Controls reference bias current to RX bandpass filters: 0: 4 uA (Reset value) Use 1 instead 1: 3 uA Note: Recommended setting 12 RXBPF_MIDCUR 0 R/W Controls reference bias current to RX bandpass filters: 0: 4 uA (Default) 1: 3.5 uA 11 LOW_LOWGAIN 1 R/W LNA low gain mode setting in AGC low gain mode. 10 MED_LOWGAIN 0 R/W LNA low gain mode setting in AGC medium gain mode. 9 HIGH_HGM 1 R/W RX Mixers high gain mode setting in AGC high gain mode. 8 MED_HGM 0 R/W RX Mixers high gain mode setting in AGC medium gain mode. 7:6 LNA_CAP_ARRAY[1:0] 1 R/W Selects varactor array setting in the LNA 0: OFF 1: 0.1pF (x2) (Nominal) 2: 0.2pF (x2) 3: 0.3pF (x2) 5:4 RXMIX_TAIL[1:0] 1 R/W Control of the receiver mixers output current. 0: 12 µA 1: 16 µA (Nominal) 2: 20 µA 3: 24 µA 3:2 RXMIX_VCM[1:0] 1 R/W Controls VCM level in the mixer feedback loop 0: 8 µA mixer current 1: 12 µA mixer current (Nominal) 2: 16 µA mixer current 3: 20 µA mixer current 1:0 RXMIX_CURRENT[1:0] 2 R/W Controls current in the mixer 0: 360 µA mixer current (x2) 1: 720 µA mixer current (x2) 2: 900 µA mixer current (x2) (Nominal) 3: 1260 µA mixer current (x2) SWRS041c Page 68 of 85 CC2420 FSCTRL (0x18) - Frequency Synthesizer Control and Status Bit 15:14 Field Name Reset R/W Description LOCK_THR[1:0] 1 R/W Number of consecutive reference clock periods with successful synchronisation windows required to indicate lock: 0: 64 1: 128 (recommended) 2: 256 3: 512 13 CAL_DONE 0 R Calibration has been performed since the last time the frequency synthesizer was turned on. 12 CAL_RUNNING 0 R Calibration status, '1' when calibration in progress and ‘0’ otherwise. 11 LOCK_LENGTH 0 R/W Synchronisation window pulse width: 0: 2 prescaler clock periods (recommended) 1: 4 prescaler clock periods 10 LOCK_STATUS 0 R Frequency synthesizer lock status: 0 : Frequency synthesizer is out of lock 1 : Frequency synthesizer is in lock 9:0 FREQ[9:0] 357 (2405 MHz) R/W Frequency control word, controlling the RF operating frequency FC. In transmit mode, the local oscillator (LO) frequency equals FC. In receive mode, the LO frequency is 2 MHz below FC. FC = 2048 + FREQ[9:0] MHz See the Frequency and Channel Programming section on page 50 for further information. SWRS041c Page 69 of 85 CC2420 SECCTRL0 (0x19) - Security Control Register Bit Field Name Reset R/W Description 15:10 - 0 W0 Reserved, write as 0 9 RXFIFO_PROTECTION 1 R/W Protection enable of the RXFIFO, see description in the RXFIFO overflow section on page 33. Should be cleared if MAC level security is not used or is implemented outside CC2420. 8 SEC_CBC_HEAD 1 R/W Defines what to use for the first byte in CBC-MAC (does not apply to CBC-MAC part of CCM): 0 : Use the first data byte as the first byte into CBC-MAC 1 : Use the length of the data to be authenticated (calculated as (the packet length field – SEC_TXL – 2) for TX or using SEC_RXL for RX) as the first byte into CBC-MAC (before the first data byte). This bit should be set high for CBC-MAC 802.15.4 inline security. 7 SEC_SAKEYSEL 1 R/W Stand Alone Key select 0 : Key 0 is used 1 : Key 1 is used 6 SEC_TXKEYSEL 1 R/W TX Key select 0 : Key 0 is used 1 : Key 1 is used 5 SEC_RXKEYSEL 0 R/W RX Key select 0 : Key 0 is used 1 : Key 1 is used 4:2 SEC_M[2:0] 1 R/W Number of bytes in authentication field for CBC-MAC, encoded as (M-2)/2 0 : Reserved 1:4 2:6 3:8 4 : 10 5 : 12 6 : 14 7 : 16 1:0 SEC_MODE[1:0] 0 R/W Security mode 0 : In-line security is disabled 1 : CBC-MAC 2 : CTR 3 : CCM SWRS041c Page 70 of 85 CC2420 SECCTRL1 (0x1A) - Security Control Register Bit Field Name Reset R/W Description 15 - 0 W0 Reserved, write as 0 14:8 SEC_TXL 0 R/W Multi-purpose length byte for TX in-line security operations: CTR : Number of cleartext bytes between length byte and the first byte to be encrypted CBC/MAC : Number of cleartext bytes between length byte and the first byte to be authenticated CCM : l(a), defining the number of bytes to be authenticated but not encrypted Stand-alone : SEC_TXL has no effect 7 - 0 W0 Reserved, write as 0 6:0 SEC_RXL 0 R/W Multi-purpose length byte for RX in-line security operations: CTR : Number of cleartext bytes between length byte and the first byte to be decrypted CBC/MAC : Number of cleartext bytes between length byte and the first byte to be authenticated CCM : l(a), defining the number of bytes to be authenticated but not decrypted Stand-alone : SEC_RXL has no effect BATTMON (0x1B) – Battery Monitor Control register Bit Field Name Reset R/W Description 15:7 - 0 W0 Reserved, write as 0 6 BATTMON_OK 1 R Battery monitor comparator output, read only. BATT_OK is valid 5 us after BATTMON_EN has been asserted and BATTMON_VOLTAGE has been programmed. 0 : Power supply < Toggle Voltage 1 : Power supply > Toggle Voltage 5 BATTMON_EN 0 R/W Battery monitor enable 0 : Battery monitor is disabled 1 : Battery monitor is enabled 4:0 BATTMON_VOLTAGE [4:0] 0 R/W Battery monitor toggle voltage. The toggle voltage is given by: V SWRS041c toggle 1.25 V 72 BATTMON_VO LTAGE 27 Page 71 of 85 CC2420 IOCFG0 (0x1C) – I/O Configuration Register 0 Bit Field Name Reset R/W Description 15:12 - 0 W0 Reserved, write as 0 11 BCN_ACCEPT 0 R/W Accept all beacon frames when address recognition is enabled. This bit should be set when the PAN identifier programmed into CC2420 RAM is equal to 0xFFFF and cleared otherwise. This bit is don't care when MDMCTRL0.ADR_DECODE = 0. 0 : Only accept beacons with a source PAN identifier which matches the PAN identifier programmed into CC2420 RAM 1 : Accept all beacons regardless of the source PAN identifier 10 FIFO_POLARITY 0 R/W Polarity of the output signal FIFO. 0 : Polarity is active high 1 : Polarity is active low 9 FIFOP_POLARITY 0 R/W Polarity of the output signal FIFOP. 0 : Polarity is active high 1 : Polarity is active low 8 SFD_POLARITY 0 R/W Polarity of the SFD pin. 0 : Polarity is active high 1 : Polarity is active low 7 CCA_POLARITY 0 R/W Polarity of the CCA pin. 0 : Polarity is active high 1 : Polarity is active low 6:0 FIFOP_THR[6:0] 64 R/W FIFOP_THR sets the threshold in number of bytes in the RXFIFO for FIFOP to go active. SWRS041c Page 72 of 85 CC2420 IOCFG1 (0x1D) – I/O Configuration Register 1 Bit Field Name Reset R/W Description 15:13 - 0 W0 Reserved, write as 0 12:10 HSSD_SRC[2:0] 0 R/W The HSSD module is used as follows: 0: Off. 1: Output AGC status (gain setting / peak detector status / accumulator value) 2: Output ADC I and Q values. 3: Output I/Q after digital down mix and channel filtering. 4: Reserved 5: Reserved 6: Input ADC I and Q values 7: Input DAC I and Q values. The HSSD module requires that the FS is up and running as it uses CLK_PRE (~150 MHZ) to produce its ~37.5 MHz data clock and serialize its output words. 9:5 SFDMUX[4:0] 0 R/W Multiplexer setting for the SFD pin. 4:0 CCAMUX[4:0] 0 R/W Multiplexer setting for the CCA pin. MANFIDL (0x1E) - Manufacturer ID, Lower 16 Bit Bit Field Name Reset R/W Description 15:12 PARTNUM[3:0] 2 R The device part number. CC2420 has part number 0x002. 11:0 MANFID[11:0] 0x33D R Gives the JEDEC manufacturer ID. The actual manufacturer ID can be found in MANIFID[7:1], the number of continuation bytes in MANFID[11:8] and MANFID[0]=1. Chipcon's JEDEC manufacturer ID is 0x7F 0x7F 0x7F 0x9E (0x1E preceded by three continuation bytes.) MANFIDH (0x1F) - Manufacturer ID, Upper 16 Bit Bit Field Name Reset R/W Description 15:12 VERSION[3:0] 3 R Version number. Current version is 3. Note that previous CC2420 versions will have lower reset values. 11:0 PARTNUM[15:4] 0 R The device part number. CC2420 has part number 0x002. FSMTC (0x20) - Finite state machine time constants Bit Field Name Reset R/W Description 15:13 TC_RXCHAIN2RX[2:0] 3 R/W The time in 5 us steps between the time the RX chain is enabled and the demodulator and AGC is enabled. The RX chain is started when the bandpass filter has been calibrated (after 6.5 symbol periods). 12:10 TC_SWITCH2TX[2:0] 6 R/W The time in advance the RXTX switch is set high, before enabling TX. In s. 9:6 TC_PAON2TX[3:0] 10 R/W The time in advance the PA is powered up before enabling TX. In s. 5:3 TC_TXEND2SWITCH[2:0] 2 R/W The time after the last chip in the packet is sent, and the TXRX switch is disabled. In s. 2:0 TC_TXEND2PAOFF[2:0] 4 R/W The time after the last chip in the packet is sent, and the PA is set in power-down. Also the time at which the modulator is disabled. In s. SWRS041c Page 73 of 85 CC2420 MANAND (0x21) - Manual signal AND override register Bit 1 Field Name Reset R/W Description 15 VGA_RESET_N 1 R/W The VGA_RESET_N signal is used to reset the peak detectors in the VGA in the RX chain. 14 BIAS_PD 1 R/W Global bias power down (1) 13 BALUN_CTRL 1 R/W The BALUN_CTRL signal controls whether the PA should receive its required external biasing (1) or not (0) by controlling the RX/TX output switch. 12 RXTX 1 R/W RXTX signal: controls whether the LO buffers (0) or PA buffers (1) should be used. 11 PRE_PD 1 R/W Powerdown of prescaler. 10 PA_N_PD 1 R/W Powerdown of PA (negative path). 9 PA_P_PD 1 R/W Powerdown of PA (positive path). When PA_N_PD=1 and PA_P_PD=1 the up-conversion mixers are in powerdown. 8 DAC_LPF_PD 1 R/W Powerdown of TX DACs. 7 XOSC16M_PD 1 R/W 6 RXBPF_CAL_PD 1 R/W Powerdown control of complex bandpass receive filter calibration oscillator. 5 CHP_PD 1 R/W Powerdown control of charge pump. 4 FS_PD 1 R/W Powerdown control of VCO, I/Q generator, LO buffers. 3 ADC_PD 1 R/W Powerdown control of the ADCs. 2 VGA_PD 1 R/W Powerdown control of the VGA. 1 RXBPF_PD 1 R/W Powerdown control of complex bandpass receive filter. 0 LNAMIX_PD 1 R/W Powerdown control of LNA, down-conversion mixers and frontend bias. 1 For some important signals the value used by analog and digital modules can be overridden manually. This is done as follows for the hypothetical important signal IS: IS_USED = (IS * IS_AND_MASK) + IS_OR_MASK, using boolean notation. The AND-mask and OR-mask for the important signals listed resides in the MANAND and MANOR registers, respectively. Examples: Writing 0xFFFE to MANAND and 0x0000 to MANOR will force LNAMIX_PD0 whereas all other signals will be unaffected. Writing 0xFFFF to MANAND and 0x0001 to MANOR will force LNAMIX_PD1 whereas all other signals will be unaffected. SWRS041c Page 74 of 85 CC2420 MANOR (0x22) - Manual signal OR override register Bit Field Name Reset R/W Description 15 VGA_RESET_N 0 R/W The VGA_RESET_N signal is used to reset the peak detectors in the VGA in the RX chain. 14 BIAS_PD 0 R/W Global Bias power down (1) 13 BALUN_CTRL 0 R/W The BALUN_CTRL signal controls whether the PA should receive its required external biasing (1) or not (0) by controlling the RX/TX output switch. 12 RXTX 0 R/W RXTX signal: controls whether the LO buffers (0) or PA buffers (1) should be used. 11 PRE_PD 0 R/W Powerdown of prescaler. 10 PA_N_PD 0 R/W Powerdown of PA (negative path). 9 PA_P_PD 0 R/W Powerdown of PA (positive path). When PA_N_PD=1 and PA_P_PD=1 the up-conversion mixers are in powerdown. 8 DAC_LPF_PD 0 R/W Powerdown of TX DACs. 7 XOSC16M_PD 0 6 RXBPF_CAL_PD 0 R/W Powerdown control of complex bandpass receive filter calibration oscillator. 5 CHP_PD 0 R/W Powerdown control of charge pump. 4 FS_PD 0 R/W Powerdown control of VCO, I/Q generator, LO buffers. 3 ADC_PD 0 R/W Powerdown control of the ADCs. 2 VGA_PD 0 R/W Powerdown control of the VGA. 1 RXBPF_PD 0 R/W Powerdown control of complex bandpass receive filter. 0 LNAMIX_PD 0 R/W Powerdown control of LNA, down-conversion mixers and frontend bias. Field Name Reset R/W Description 15:12 - 0 W0 Reserved, write as 0 11 VGA_GAIN_OE 0 R/W Use the VGA_GAIN value during RX instead of the AGC value. 10:4 VGA_GAIN [6:0] 0x7F R/W When written, VGA manual gain override value; when read, the currently used VGA gain setting. 3:2 LNAMIX_GAINMODE_O [1:0] 0 R/W LNA / Mixer Gain mode override setting LNAMIX_GAINMODE [1:0] 3 AGCCTRL (0x23) - AGC Control Bit 1:0 0 : Gain mode is set by AGC algorithm 1 : Gain mode is always low-gain 2 : Gain mode is always med-gain 3 : Gain mode is always high-gain R Status bit, defining the currently selected gain mode selected by the AGC or overridden by the LNAMIX_GAINMODE_O setting. SWRS041c Page 75 of 85 CC2420 AGCTST0 (0x24) - AGC Test Register 0 Bit Field Name Reset R/W Description 15:12 LNAMIX_HYST[3:0] 3 R/W Hysteresis on the switching between different RF front-end gain modes, defined in 2 dB steps 11:6 LNAMIX_THR_H[5:0] 25 R/W Threshold for switching between medium and high RF frontend gain mode, defined in 2 dB steps 5:0 LNAMIX_THR_L[5:0] 9 R/W Threshold for switching between low and medium RF frontend gain mode, defined in 2 dB steps AGCTST1 (0x25) - AGC Test Register 1 Bit Field Name Reset R/W Description 15 - 0 W0 Reserved, write as 0 14 AGC_BLANK_MODE 0 R/W Set the VGA blanking mode when switching out a gain stage When VGA_GAIN_OE = 0: 0 : Blanking is performed when the AGC algorithm switches out one or more 14dB gain stages. 1 : Blanking is never performed. When VGA_GAIN_OE = 1: Blanking is performed when AGC_BLANK_MODE=1 13 PEAKDET_CUR_BOOST 0 R/W Doubles the bias current in the peak-detectors in-between the VGA stages when set. 12:11 AGC_SETTLE_WAIT[1:0] 1 R/W Timing for AGC to wait for analog gain to settle. 10:8 AGC_PEAK_DET_MODE [2:0] 0 R/W Sets the AGC mode for use of the VGA peak detectors: AGC_WIN_SIZE[1:0] 1 7:6 Bit 2 : Digital ADC peak detector enable / disable Bit 1 : Analog fixed stages peak detector enable / disable Bit 0 : Analog variable gain stage peak detector enable / disable R/W Window size for the accumulate and dump function in the AGC. 0 : 8 samples 1 : 16 samples 2 : 32 samples 3 : 64 samples 5:0 AGC_REF[5:0] 20 R/W Target value for the AGC control loop, given in 2 dB steps. Reset value corresponds to approximately 25% of the ADC dynamic range in reception. AGCTST2 (0x26) - AGC Test Register 2 Bit Field Name Reset R/W Description 15:10 - 0 W0 Reserved, write as 0 9:5 MED2HIGHGAIN[4:0] 9 R/W MED2HIGHGAIN sets the difference in the receiver LNA/MIXER gain from medium gain mode to high gain mode, used by the AGC for setting the correct front-end gain mode. 4:0 LOW2MEDGAIN[4:0] 10 R/W LOW2MEDGAIN sets the difference in the receiver LNA/MIXER gain from low gain mode to medium gain mode, used by the AGC for setting the correct front-end gain mode. SWRS041c Page 76 of 85 CC2420 FSTST0 (0x27) - Frequency Synthesizer Test Register 0 Bit Field Name Reset R/W Description 15:12 - 0 W0 Reserved, write as 0 11 VCO_ARRAY_SETTLE_LONG 0 R/W When '1' this control bit doubles the time allowed for VCO settling during VCO calibration. 10 VCO_ARRAY_OE 0 R/W VCO array manual override enable. 9:5 VCO_ARRAY_O[4:0] 16 R/W VCO array override value. 4:0 VCO_ARRAY_RES[4:0] 16 R The VCO array result holds the register content of the most recent calibration. FSTST1 (0x28) - Frequency Synthesizer Test Register 1 Bit Field Name Reset R/W Description 15 VCO_TX_NOCAL 0 R/W 0 : VCO calibration is always performed when going to RX or when going to TX. 1 : VCO calibration is only performed when going to RX or when using the STXCAL command strobe 14 VCO_ARRAY_CAL_LONG 1 R/W When ‘1’ this control bit doubles the time allowed for VCO frequency measurements during VCO calibration. 0 : PLL Calibration time is 37 us 1 : PLL Calibration time is 57 us 13:10 VCO_CURRENT_REF[3:0] 4 R/W The value of the reference current calibrated against during VCO calibration. 9:4 VCO_CURRENT_K[5:0] 0 R/W VCO current calibration constant. (Current B override value when FSTST2.VCO_CURRENT_OE=1.) 3 VC_DAC_EN 0 R/W Controls the source of the VCO VC node in normal operation (TOPTST.VC_IN_TEST_EN=0): 0: Loop filter (closed loop PLL) 1: VC DAC (open loop PLL) 2:0 VC_DAC_VAL[2:0] 2 R/W VC DAC output value FSTST2 (0x29) - Frequency Synthesizer Test Register 2 Bit Field Name Reset R/W Description 15 - 0 W0 Reserved, write as 0. 14:13 VCO_CURCAL_SPEED[1:0] 0 R/W VCO current calibration speed: 0: Normal 1: Double speed 2: Half speed 3: Undefined. 12 VCO_CURRENT_OE 0 R/W VCO current manual override enable. 11:6 VCO_CURRENT_O[5:0] 24 R/W VCO current override value (current A). 5:0 VCO_CURRENT_RES[5:0] 32 R The VCO current result holds the register content of the most recent calibration. SWRS041c Page 77 of 85 CC2420 FSTST3 (0x2A) - Frequency Synthesizer Test Register 3 Bit Field Name Reset R/W Description 15 CHP_CAL_DISABLE 1 R/W Disable charge pump during VCO calibration when set. 14 CHP_CURRENT_OE 0 R/W Charge pump current override enable 0 : Charge pump current set by calibration 1 : Charge pump current set by START_CHP_CURRENT 13 CHP_TEST_UP 0 R/W Forces the CHP to output "up" current when set 12 CHP_TEST_DN 0 R/W Forces the CHP to output "down" current when set 11 CHP_DISABLE 0 R/W Set to manually disable charge pump by masking the up and down pulses from the phase-detector. 10 PD_DELAY 0 R/W Selects short or long reset delay in phase detector: 0: Short reset delay 1: Long reset delay 9:8 CHP_STEP_PERIOD[1:0] 2 R/W The charge pump current value step period: 0: 0.25 us 1: 0.5 us 2: 1 us 3: 4 us 7:4 STOP_CHP_CURRENT[3:0] 13 R/W The charge pump current to stop at after the current is stepped down from START_CHP_CURRENT after VCO calibration is complete. The current is stepped down periodically with intervals as defined in CHP_STEP_PERIOD. 3:0 START_CHP_CURRENT[3:0] 13 R/W The charge pump current to start with after VCO calibration is complete. The current is then stepped down periodically to the value STOP_CHP_CURRENT with intervals as defined in CHP_STEP_PERIOD. Also used for overriding the charge pump current when CHP_CURRENT_OE=’1’ RXBPFTST (0x2B) - Receiver Bandpass Filters Test Register Bit Field Name Reset R/W Description 15 - 0 W0 Reserved, write as 0. 14 RXBPF_CAP_OE 0 R/W RX bandpass filter capacitance calibration override enable. 13:7 RXBPF_CAP_O[6:0] 0 R/W RX bandpass filter capacitance calibration override value. 6:0 RXBPF_CAP_RES[6:0] 0 R RX bandpass filter capacitance calibration result. 0: Minimum capacitance in the feedback. 1: Second smallest capacitance setting. … 127: Maximum capacitance in the feedback. FSMSTATE (0x2C) - Finite state machine information Bit Field Name Reset R/W Description 15:6 - 0 W0 Reserved, write as 0. 5:0 FSM_CUR_STATE[5:0] 0 R Provides the current state of the FIFO and Frame Control (FFCTRL) finite state machine. See the Radio control state machine section on page 43 for details. SWRS041c Page 78 of 85 CC2420 ADCTST (0x2D) - ADC Test Register Bit 15 Field Name Reset R/W Description ADC_CLOCK_DISABLE 0 R/W ADC Clock Disable 0 : Clock enabled when ADC enabled 1 : Clock disabled, even if ADC is enabled 14:8 ADC_I[6:0] 0 R Read the current ADC I-branch value. 7 - 0 W0 Reserved, write as 0. 6:0 ADC_Q[6:0] 0 R Read the current ADC Q-branch value. DACTST (0x2E) - DAC Test Register Field Name Reset R/W Description 15 - 0 W0 Reserved, write as 0. 14:12 DAC_SRC[2:0] 0 R/W The TX DACs data source is selected by DAC_SRC according to: Bit 0: Normal operation (from modulator). 1: The DAC_I_O and DAC_Q_O override values below.2: From ADC, most significant bits 3: I/Q after digital down mixing and channel filtering. 4: Full-spectrum White Noise (from CRC) 5: From ADC, least significant bits 6: RSSI / Cordic Magnitude Output 7: HSSD module. This feature will often require the DACs to be manually turned on in MANOR and TOPTST.ATESTMOD_MODE=4. 11:6 DAC_I_O[5:0] 0 R/W I-branch DAC override value. 5:0 DAC_Q_O[5:0] 0 R/W Q-branch DAC override value. SWRS041c Page 79 of 85 CC2420 TOPTST (0x2F) - Top Level Test Register Bit Field Name Reset R/W Description 15:8 - 0 W0 Reserved, write as 0. 7 RAM_BIST_RUN 0 R/W Enable BIST of the RAM 0 : RAM BIST disabled, normal operation 1 : RAM BIST Enabled. Result output to pin, as set in IOCFG1. 6 TEST_BATTMON_EN 0 R/W Enable test output of the battery monitor. 5 VC_IN_TEST_EN 0 R/W When ATESTMOD_MODE=7 this controls whether the ATEST2 in is used to output the VC node voltage (0) or to control the VC node voltage (1). 4 ATESTMOD_PD 1 R/W Powerdown of analog test module. 0 : Power up 1 : Power down 3:0 ATESTMOD_MODE[3:0] 0 When ATESTMOD_PD=0, the function of the analog test module is as follows: 0: Outputs “I” (ATEST1) and “Q” (ATEST2) from RxMIX. 1: Inputs “I” (ATEST2) and “Q” (ATEST1) to BPF. 2: Outputs “I” (ATEST1) and “Q” (ATEST2) from VGA. 3: Inputs “I” (ATEST2) and “Q” (ATEST1) to ADC. 4: Outputs “I” (ATEST1) and “Q” (ATEST2) from LPF. 5: Inputs “I” (ATEST2) and “Q” (ATEST1) to TxMIX. 6: Outputs “P” (ATEST1) and “N” (ATEST2) from Prescaler. Must be terminated externally. 7: Connects TX IF to RX IF and simultaneously the ATEST1 pin to the internal VC node (see VC_IN_TEST_EN). 8. Connect ATEST1 (input) to ATEST2 (output) through single2diff and diff2single buffers, used for measurements on the test-interface RESERVED (0x30) - Reserved register containing spare control and status bits Bit 15:0 Field Name Reset R/W Description RES[15:0] 0 R/W Reserved for future use TXFIFO (0x3E) – Transmit FIFO Byte register Bit 7:0 Field Name Reset R/W Description TXFIFO[7:0] 0 W Transmit FIFO byte register, write only. Reading the TXFIFO is only possible using RAM read. Note that the crystal oscillator must be running for writing to the TXFIFO. RXFIFO (0x3F) – Receive FIFO Byte register Bit 7:0 Field Name Reset R/W Description RXFIFO[7:0] 0 R/W Receive FIFO byte register, read / write. Note that the crystal oscillator must be running for accessing the RXFIFO. SWRS041c Page 80 of 85 CC2420 38 Test Output Signals The two digital output pins CCA and SFD, can be set up to output test signals defined by IOCFG1.CCAMUX and IOCFG1.SFDMUX. This is summarized in Table 12 and Table 13 below. CCAMUX Signal output on CCA pin Description 0 CCA Normal operation 1 ADC_Q[0] ADC, Q-branch, LSB used for random number generation 2 DEMOD_RESYNC_LATE High one 16 MHz clock cycle each time the demodulator resynchronises late 3 LOCK_STATUS Lock status, same as FSCTRL.LOCK_STATUS 4 MOD_CHIPCLK Chip rate clock signal during transmission 5 MOD_SERIAL_CLK Bit rate clock signal during transmission 6 FFCTRL_FS_PD Frequency synthesizer power down, active high 7 FFCTRL_ADC_PD ADC power down, active high 8 FFCTRL_VGA_PD VGA power down, active high 9 FFCTRL_RXBPF_PD Receiver bandpass filter power down, active high 10 FFCTRL_LNAMIX_PD Receiver LNA / Mixer power down, active high 11 FFCTRL_PA_P_PD Power amplifier power down, active high 12 AGC_UPDATE High one 16 MHz clock cycle each time the AGC updates its gain setting 13 VGA_PEAK_DET[1] VGA Peak detector, gain stage 1 14 VGA_PEAK_DET[3] VGA Peak detector, gain stage 3 15 AGC_LNAMIX_GAINMODE[1] RF receiver front-end gain mode, bit 1 16 AGC_VGA_GAIN[1] VGA gain setting, bit 1 17 VGA_RESET_N VGA peak-detector reset sign, active low. 18 - Reserved 19 - Reserved 20 - Reserved 21 - Reserved 22 - Reserved 23 CLK_8M 8 MHz clock signal output 24 XOSC16M_STABLE 16 MHz crystal oscillator stabilised, same as the status bit in Table 5 25 FSDIG_FREF Frequency synthesizer, 4 MHz reference signal 26 FSDIG_FPLL Frequency synthesizer, 4 MHz divided signal 27 FSDIG_LOCK_WINDOW Frequency synthesizer, lock window 28 WINDOW_SYNC Frequency synthesizer, synchronized lock window 29 CLK_ADC ADC clock signal 1 30 ZERO Low 31 ONE High Table 12. CCA test signal select table SWRS041c Page 81 of 85 CC2420 SFDMUX Signal output on SFD pin Description 0 SFD Normal operation 1 ADC_I[0] ADC, I-branch, LSB used for random number generation 2 DEMOD_RESYNCH_EARLY High one 16 MHz clock cycle each time the demodulator resynchronises early 3 LOCK_STATUS Lock status, same as FSCTRL.LOCK_STATUS 4 MOD_CHIP Chip rate data signal during transmission 5 MOD_SERIAL_DATA_OUT Bit rate data signal during transmission 6 FFCTRL_FS_PD Frequency synthesizer power down, active high 7 FFCTRL_ADC_PD ADC power down, active high 8 FFCTRL_VGA_PD VGA power down, active high 9 FFCTRL_RXBPF_PD Receiver bandpass filter power down, active high 10 FFCTRL_LNAMIX_PD Receiver LNA / Mixer power down, active high 11 FFCTRL_PA_P_PD Power amplifier power down, active high 12 VGA_PEAK_DET[0] VGA Peak detector, gain stage 0 13 VGA_PEAK_DET[2] VGA Peak detector, gain stage 2 14 VGA_PEAK_DET[4] VGA Peak detector, gain stage 4 15 AGC_LNAMIX_GAINMODE[0] RF receiver front-end gain mode, bit 0 16 AGC_VGA_GAIN[0] VGA gain setting, bit 0 17 RXBPF_CAL_CLK Receiver bandpass filter calibration clock 18 - Reserved 19 - Reserved 20 - Reserved 21 - Reserved 22 - Reserved 23 - Reserved 24 PD_F_COMP Frequency synthesizer frequency comparator value 25 FSDIG_FREF Frequency synthesizer, 4 MHz reference signal 26 FSDIG_FPLL Frequency synthesizer, 4 MHz divided signal 27 FSDIG_LOCK_WINDOW Frequency synthesizer, lock window 28 WINDOW_SYNC Frequency synthesizer, synchronized lock window 29 CLK_ADC_DIG ADC clock signal 2 30 ZERO Low 31 ONE High Table 13. SFD test signal select table SWRS041c Page 82 of 85 CC2420 39 Soldering information Recommended soldering profile is according to IPC/JEDEC J-STD-020C. Please see the CC2420EM reference design for details on layout. SWRS041c Page 83 of 85 CC2420 40 General Information 40.1 Document History Revision Date Description/Changes SWRS041c 2013-02-20 Changed packaging and orderable information to reflect change to RGZ package. SWRS041b 2007-03-19 Slightly changed optimum load impedance on Page 9 and 19 to better describe the Application circuit. SWRS041a 2006-12-18 Updated ordering information. Updated address information. Typical data latency changed from 2 to 3 us. Updates reflecting the programmable polarity of FIFO, FIFOP, SFD and CCA pins. Clarification relating to VREG_EN as digital input. BATT_OK changed to BATTMON_OK for consistency. MANFIDH.VERSION register, reset value changed to ”current version is 3”. Added reset values for several registers. Some typographical changes. Removed Chipcon specific Disclaimer, Trademarks and Life Support Policy sections. SWRS041 2006-04-06 Ordering part number changed from CC2420-RTB2 and CC2420-RTR2 to CC2420ZRTB1 and CC2420Z-RTR1 respectively. 2005-10-03 Important: New recommended setting for RXBPF_LOCUR in RXCTRL1 (0x17) use 1 instead of reset value 0. Updated address information. Added new balun circuit with transmission lines in section Application Circuit. Updated electrical specifications with measured data on CC2420 EM with new balun. Updated values and figure for suggested application circuit with folded dipole antenna. Corrected values for capacitors in Table 2, discrete balun. Added data latency figure in receiver specification. Updated crystal oscillator start up time. Updated PLL loop filter bandwidth. Updated adjacent channel rejection figures. Updated current consumption for RX mode. Typographical errors corrected in text and figures. Removed comment about tuning capacitor for crystal oscillator. Added statement that RAM access shall not be used for FIFO access. Added more details about RSSI. Clarified the interpretation of a programmed synchronisation word. Updated purchasing information. Updated soldering standard. Added chapter numbering and split table for electrical specifications for readability. Gathered and added information related to pin configurations in section 13. Included TX_UNDERFLOW and RX_UNDERFLOW in state diagram. Disclaimer updated to include Z-stack TM information. Product status changed to “Full Production”. (1.4) 1.3 SWRS041c Page 84 of 85 CC2420 Revision Date Description/Changes 1.2 2004-06-09 Output power range: 24 dB (was 40 dB). Deleted option for single ended external PA. Adjacent channel rejection corrected to 46 dB for + 5MHz (was 39 dB), 39 dB for –5 MHz (was 46 dB) 58 dB for +10 MHz (was 53 dB) and 55 dB for-10 MHz (was 57 dB). “image channel” deleted in text for In band spurious reception. Revision for reference [1] updated. CSMA-CA added to abbreviations. Schematic view of the IEEE 802.15.4 Frame Format corrected, address field 0 to 20 bits. Changed blocking specifications to relate to EN 300 440 class 2. Updated addresses for Chipcon offices. Added section Operating Conditions. Section RAM access: A6:0 (LSB). IOCFG0.BCN_ACCEPT bit added and described in section Address recognition and the IOCFG0 register. The previous IDLE mode has been renamed to power down to be consistent with other Chipcon data sheets. Three power modes defined: Voltage regulator off (OFF), Power down (PD) (Voltage regulator enabled), IDLE (XOSC running) and used throughout the document. Default TXMIXBUF_CUR[1:0] in table for TXCTRL set to 2. Added information: compliance with EN 300 328 og EN 300 440 (Class 2). Added more information about FIFOP in section Receive mode. Removed text about SO programmable pull up from entire document. In Voltage regulator section of Electrical Specifications: voltage regulator may only supply CC2420. MANFIDH.VERSION register, changed to ”current version is 2”. Included package height in package drawing. Included layout drawing for package. Power supply pins defined clearer in Absolute maximum ratings. Third harmonic level corrected to –51dBm in Electrical specifications, second harmonic to –37dBm. Table with Crystal oscillator component values corrected. Link to reference [3] corrected. Corrected spelling grammar and references to tables and figures. Figure showing SmartRF Studio user interface included. Added figure to describe pin activity during RXFIFO read out. Added description on how to connect pins when not using internal regulator. 1.1 2004-03-22 Application circuits: Pin 20 and pin 37 connected to 1.8 V from VREG_OUT. IOCFG0.SO_PULLUP deleted. Added document history table. 1.0 2003-11-17 Initial release. SWRS041c Page 85 of 85 PACKAGE OPTION ADDENDUM www.ti.com 25-Oct-2013 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty 52 Eco Plan Lead/Ball Finish MSL Peak Temp (2) (6) (3) Op Temp (°C) Device Marking Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR -40 to 85 CC2420 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR -40 to 85 CC2420 (4/5) CC2420-RTB1 NRND VQFN RTC 48 CC2420-RTR1 OBSOLETE VQFN RTC 48 CC2420RGZR ACTIVE VQFN RGZ 48 2500 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR -40 to 85 CC2420 CC2420RGZT ACTIVE VQFN RGZ 48 250 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR -40 to 85 CC2420 CC2420Z-RTB1 NRND VQFN RTC 48 52 Green (RoHS & no Sb/Br) CU NIPDAU Level-3-260C-168 HR -40 to 85 CC2420 CC2420Z-RTR1 OBSOLETE VQFN RTC 48 TBD Call TI Call TI -40 to 85 (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. 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Addendum-Page 2 PACKAGE MATERIALS INFORMATION www.ti.com 15-Jul-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant CC2420RGZR VQFN RGZ 48 2500 330.0 16.4 7.3 7.3 1.5 12.0 16.0 Q2 CC2420RGZT VQFN RGZ 48 250 330.0 16.4 7.3 7.3 1.5 12.0 16.0 Q2 Pack Materials-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 15-Jul-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) CC2420RGZR VQFN RGZ 48 2500 336.6 336.6 28.6 CC2420RGZT VQFN RGZ 48 250 336.6 336.6 28.6 Pack Materials-Page 2 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. 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